This commit introduce a full redesign of all JS views.  We started
basically from scratch.  The goal was to unify all the various views
under a common framework, to make them testable, to make then usable in
different conditions (in studio, or in the frontend), and to make our
lives easier.

Some important points are:
- we introduced new coding guidelines (camelCase, 80 chars width, ...)
- we have a brand new testing framework (still QUnit based)
- kanban view moved to the web addon
- calendar view (formerly web_calender) moved to web as well
- the tree view was removed
- all new code should be documented

We hope that this code is the start of a new era for the Odoo web
client, we want to have a high quality codebase, well documented, well
tested, well designed.

Work done by the framework team: mostly aab, ged, chm, dmo, qsm

The editable list has a `is_valid` method which checks that all the
records it contains have valid data. The problem is that it was
considering that all the records in the `dataset.cache` were part of
the x2x field the editable list is working with. This is wrong as the
`dataset.cache` can contain information which are not part of the
editable list anymore.
See the commit which introduced the use of the `dataset.cache`:
a9d20d9fa04b1dbb350663652e0996e258ac6d31

This was causing issues with rare cases of an editable list which
contains another editable list (even invisible) which was sharing
common information with its parent editable list.

opw-710627

The revision
dd657c42f7cbac01294ef794bf0e697ed495c722

intended to give the possibility to add an existing
record to a many2many list even without the `create` access
on the model of this record.
This is accepted by the ORM, as there is no need of the create
right on the model, only the write on the source model on which
the many2many field is.

The revision has as unexpected side effect to remove the possibility
to manually set `create="0"` on the tree of a many2many field,
to hide the "add an item" of the list view.

As this last feature is more important, we therefore revert this.

We will provide another solution for the above issue.
We think about forcing what the view definition says, so if you
set create="1" on the view, it will display the "add an item" link
in any case, even if you do not have the access right to do it.
This would allow to display the link for the above case, and in case
you actually do not have the access right, and this is an error
in the view definition, you will have an access error raised anyway.

opw-708310

One can add an item in a Many2Many without creating it, so the action
should be available. However, if the create action is not allowed, there
is no 'Create' button in the SelectCreateDialog.