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

When the webclient calls do_action from the app_switcher, it toggles it when
the returned deferred is resolved.

The logout client action didn't return anything, so when logging out from the
app switcher, the webclient directly toggled the app_switcher and displayed
the last opened action if any, and a gray screen otherwise.

This commit makes the client action return a deferred which is never resolved,
so the app_switcher isn't toggled when logging out.

Avoid duplicating web addon in enterprise by extracting a common basis.
Enterprise features stay in enterprise, but use that common basis.

Mainly:
 - JS refactoring and linting
 - Conversion of .sass into .less split into multiple files
 - Templates cleaning and DOM simplification
 - Re-generation of web.pot, and update of .po files

One will still be able to chat in chat windows during long RPCs...

to compute the offset of a DOM element

from 500 to 1000, as requested by fp

The main purpose of this commit is to be consistent with the enterprise edition,
in which the event 'DOM_updated' is triggered when new content is inserted in
the DOM. This way, addons that need to know when a view has been attached in the DOM
(e.g. web_tip) can listen to this event and will work fine with both editions
of the web addon.

With the actual structure of the webclient (action_manager, view_manager),
there is no easy way to decide whether or not a view is attached in the DOM,
because every rendering is performed in a detached element. For instance,
when a view_manager instantiates a new view, it appends it in its $el once
the view is ready, but it can't know if its $el is attached in the DOM (it is
only the case if the view_manager is the current action of the action manager).

This rev. introduces utility functions to centralize the appending/prepending of
content, so that an event can be triggered (at a unique place) when the content
is really in the DOM. These functions are used by the the action_manager and the
view_manager.

Another change is that the action_manager keeps the view_manager informed when
they are attached in/detached from the DOM, through the variable is_in_DOM.