Fix GitLab && Gitorious importers. Hide already imported projects

Fixes #2060

See merge request !1594

Correctly set default projects limit for new users.

See #2014.

Note that the projects limit still isn't retroactively applied to existing users (probably as intended)

See merge request !1547

Prevent another migration from failing due to indirect use of model columns not yet created

See https://github.com/gitlabhq/gitlabhq/issues/8817#issuecomment-76007077

cc @marin

See merge request !1597

Update gitlab-shell version in installation and update documentation

installation was totally off compared to the update document. The update
document was slightly off (rake gitlab:check excpects 2.5.4 and not
2.5.3)

access

Bump gitlab-shell to 2.5.4

For #2042

See merge request !1584

Fix links to issues if instance is using relative urls.

Fix for https://github.com/gitlabhq/gitlabhq/issues/8767

See merge request !1574

Changes for 7.8 RC5

See merge request !1566

Change check to only swap static middleware when it's enabled.

Fixes problem with #1553.

cc @marin

See merge request !1565

Changes for 7.8.rc4

See merge request !1564

Fix note attachments XSS and access control

Replaces the reverted #1528, as proposed in https://gitlab.com/gitlab-org/omnibus-gitlab/issues/434, as discussed with @dzaporozhets and as summarized in #2032.

@marin Could you take a look at the nginx config and apply it to Omnibus once this gets merged?

See merge request !1553

Improve web hooks

* add git_http_url and git_ssh_url to project web hook
* add visibility_level to project web hook
* add documentation about project visibility_level in API

Fixes #2018, #2030

cc @sytse

See merge request !1560

Conflicts:
	app/models/user.rb

Code from master to 7-8-stable for RC2

See merge request !1544

Conflicts:
	app/models/user.rb