Catalog does not need "resource_uid" when it requested for
"resource_use_uid", so don't spend time computing it.

Allows searching for, for example:
  some_relation_uid=[123, None]
without having to resort to:
  ComplexQuery(
    SimpleQuery(some_relation_uid=123),
    SimpleQuery(some_relation_uid=None),
    logical_operator='OR',
  )

To prepare for extension.

Otherwise, some otherise-matching predicates may be excluded from the
search, and will not be applied.

Query has a higher overhead than SimpleQuery, and should be avoided
wherever possible.
Also, get rid of two unnecessary intermediate ComplexQuery levels.
There are a few remaining Query uses here, which should go away soon.

Also, use valid base categories for
not-in-preferred_predicate_category_list test.
Also, improve coding style.
Also, after changing preferred predicate category list, only reindex
the module containing predicates instead of the whole site, to reduce
test duration.

This ZSQLMethod is shadowing the one ERP5Catalog is trying to use, and
it has a table list incompatible in 2 ways:
- it joins again with catalog, despite only being used to pick the uid,
  which ERP5Catalog stopped doing for auto-generated related keys
- it is actually a chained related key: resource, then use. But
  "resource_use" exists as a Base Category, and is accessible (but broken
  until this change) as "default_resource_use_uid" (for example).

aggregate_uid can be auto-generated with one less join, and chosen
ZSQLMethod name gets in the way of auto-generated related key
(default_aggregate_uid and the like).

* Remove include_empty_item: We always want an empty item in dialogs
* Remove include_gap_in_path: This was always true

simplify code a little bit.

* There was another level of cache in Account_hashGapItemList
* Category title was used in AccountModule_getAvailableGapList

Unlike other database adaptors, memcache adaptors can be shared among
transactions. So pool them in order to reduce the number of connections
established to memcached servers. And as the connections handle
thread-safety internally (by inheriting from threading.local), threads
can share the same connection instance.
Also, do not create a new connector each time we get disconnected, just
reconnect.
Also, memcached internally retries connection, so no need to retry it
ourselves.
Also, do not log when failing to update & delete entries in cache
server: this is a racy cache, each read much be checked anyway, so
failed writes are just business as usual.
Also, document a bit more why we catch "any" exception happening during
finish, and specify base exception class following python coding best
practices.
Also, use named constant for loggin levels for remaining log directives.
Also, display traceback when catching a connection issue during
__getitem__, as the original exception gets converted into a KeyError.

/reviewed-on nexedi/erp5!305

By default in ERP5 all fields are not mandatory

Add transparent SVG and PNG icons to the manifest,
rename all functions following the Nexedi conventions,
link to the TodoMVC homepage, move Handlebars template to head,
and rename all files from tutorial_officejs_* to officejs_todomvc_*.

Fixes failing tests because of always showing "No work to be done" in worklist (lazy bug)

Test Results 20170621-6D7F8E4B

/reviewed-on nexedi/erp5!304

/reviewed-on nexedi/erp5!303

/reviewed-on nexedi/erp5!302

Name is unchanged, but it will use
Products.ERP5Type.Utils.checkPythonSourceCode which uses pylint.

The condition for an organisation to be able to use bank account from
other organisations higher in the group hierarchy should not be the
presence of bank account in this organisation, but whether or not it
acts as an independant accounting entity, and this is defined by the
presence of accounting periods.

@Tyagov @luke 

/reviewed-on nexedi/erp5!288