Until now, standalone subsystem was started as a daemon first time a terminal
was openned and since it was running as daemon, stopping the theia instance
did not stop any of the services running in the embedded slapos.

Before nexedi/slapos.core!265 there was
two supervisor running as daemon:
 - ~/srv/slapos/etc/supervisord.conf which runs slapos proxy etc
 - ~/srv/slapos/inst/etc/supervisord.conf with runs instances in the embedded
   slapos
After, the second one runs as a service in the first one, but the first one
was still running as daemon.

This changes so that the first supervisor runs as a service managed by the
Theia instance, so stopping Theia instance will effectively stop the services.

When upgrading, running instances should continue to run as detached. To
attach them to the new service, procedure could be something like this

Stop supervisors inside Theia instance:

  supervisorctl -c ~/srv/slapos/etc/supervisord.conf shutdown
  supervisorctl -c ~/srv/slapos/inst/etc/supervisord.conf shutdown

Restart slappartX:slapos-standalone-instance-XXX-on-watch from host slapos

Prevent this kind of errors when first installation fail:

    Error: [Errno 13] Permission denied: 'parts/python-language-server/bin/activate'

by using --clear the virtualenv is recreated from scratch if the command failed
for some reason.

+minor cleanups user section was not used

See https://github.com/eclipse-theia/theia/blob/v1.5.0/CHANGELOG.md#v150---27082020

Use newer nodejs as per requirement

Use vscode extensions for json and plantuml

so that theia can use a local installation of rust using rustup

The version from theia images does not support running from a plugin
installed in a read only folder, this newest version seem to work.

Also set the required java.home setting

So that gitlens extension (which can be installed per-workspace) knows
how to open files from lab.nexedi.com in browser

so that we can easily use python version 2 or 3 during development and
local testing.

This python is not directly usable with python extension, pip needs to
be installed as user, following:
https://pip.pypa.io/en/stable/installing/#installing-with-get-pip-py

so that frontend requests are requested as theia computer partition.
Practically this means that if theia is installed on slapos master,
frontend requests for slapos inside theia partition will be requested as
this theia instance.

So that parts are shared when we install ERP5 in theia

Not much tested but it looks working

Even if we don't use this, the debug pane cause an error when jdk is not
installed

Some optional extensions installable from the registry (like the XML
supports from redhat) also need java and it's better to have something
to edit XML

This reverts commit 7e3bc5ee.

Theia does not seem to be ready for this version, several things are not
working:
 - selecting another python interpreter
 - linting in the editor
 - at startup there's always a "Python is not installed.Please download
and install Python before using the extension." warning . I think this
happened sometimes with the previous version too.

jedi was working fine, but too maybe critical features are broken.

gowork include gcc's location, which can be /usr/bin when system gcc was
selected.

for better experience in the terminal

To remove GIT_EXEC_PATH from environment as this can break running
buildout with slapos.recipe.build:gitclone sections using an
incompatible git version

because python-language-server-requirements.txt contains a git URL

includes vsx registry and our resolution fixes

TODO: There are still direct references to specific version of Python in:
  - slapos component
  - bazel templates
  - nextcloud & theia SR

vscode extensions can no longer be installed from marketplace, but we
can download extensions at installation time.
Install ms-python extension so that we can have good developer
experience with python out of the box.

installing vscode-ripgrep creates a folder in temporary directory, but
never removes it.

On our test nodes it was observed that a first testnode running installs
and create this folder in /tmp/ then another testnode running as another
unix user installs and we had this error:

    Command: node ./lib/postinstall.js
    Arguments:
    Directory: /srv/slapgrid/slappart13/srv/testnode/cqg/inst/test0-0/tmp/soft/c3f3d686d3e77f9e5c20a555a2698c98/parts/theia/node_modules/vscode-ripgrep
    Output:
    Finding release for v11.0.1-2
    GET https://api.github.com/repos/microsoft/ripgrep-prebuilt/releases/tags/v11.0.1-2
    Downloading from https://api.github.com/repos/microsoft/ripgrep-prebuilt/releases/assets/13800816
    Downloading to /tmp/vscode-ripgrep-cache-1.5.7/ripgrep-v11.0.1-2-x86_64-unknown-linux-musl.tar.gz
    Download options: {"headers":{"user-agent":"vscode-ripgrep","accept":"application/octet-stream"}}
    events.js:167
        throw er; // Unhandled 'error' event
        ^

    Error: EACCES: permission denied, open '/tmp/vscode-ripgrep-cache-1.5.7/ripgrep-v11.0.1-2-x86_64-unknown-linux-musl.tar.gz'
    Emitted 'error' event at:
        at fs.open (internal/fs/streams.js:250:12)
        at FSReqWrap.oncomplete (fs.js:145:20)
    info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
    theia: Non zero exit code (1) while running command.
    While:
    Installing theia.
    Error: Non zero exit code (1) while running command.

/reviewed-on nexedi/slapos!668

This runs in a go workspace, but we don't need to always have the
(gowork) marker.

if yarn.lock is changed, part should be re-installed. This is only
useful during development.

- exclude .pyc in files list
- exclude .env for virtualenv
- don't watch git (not sure it's really needed)
- use 2 spaces on editors
- use Vifib's plantuml service
- use Ctrl for multi cursor (for chromeos where alt is right click)

Also stop including python, as we can use vscode python instead.
Add a README to describe how to do this.