[IMP] Web et al.: unique main ControlPanel

A unique main ControlPanel is instantiated by the ActionManager and it
is updated each time the state changes (i.e. when an action is performed
on the ActionManager or when switch_mode() is called on the ViewManager).

Introduction of State classes to facilitate the way of restoring
previously rendered states in ControlPanel. The notion of widgets
previously used in the ActionManager is now encapsulated in the notion
of states.

The search() function has been moved from ControlPanel to ViewManager as
it makes more sense like this.

The ViewManager doesn't have the reference to the ControlPanel but
rather communicate with it through a dedicated bus.

Some refactoring has been done on the ControlPanel as well so that it
doesn't need to know the ActionManager and the current Action anymore
(it communicates with the AM with events, and it updates itself using
information passed in arguments).

Improves the way the ViewManager requests the ControlPanel to
instantiate a SearchView, and how it waits for this SearchView to be
corretly loaded.

Move back the views logic to the ViewManager which directly asks
the ControlPanel to render the buttons and switch-buttons areas with
the views passed in arguments.

Removes option replace_breadcrumb in push_state() of ActionManager as it
is not used.

Side changes:
* Account: account_widget.js:
    Adapt code to retrieve the current state of the ActionManager.
    Required due to the introduction of State classes that encapsulate
    the notions of widgets and inner_widget in the ActionManager.
* Board: dashboard.js:
    Some refactoring to adapt the code according to the new Widgets
    structure. Several dependencies (e.g. searchview, action) were
    unnecessary. Do not append the "add to dashboard" option to the
    Favorite menu if there is no ViewManager available (e.g. in
    Messaging) instead of hidding it with a CSS rule, as a ViewManager
    required to retrieve the active_view.
* Google_spreadsheet: search.js:
    Change the way to retrieve the list_view_id s.t. it does not rely on
    parent of the SearchView anymore.
* Web: search.js:
    Change the way to retrieve the title in search.js for Favorites s.t.
    it does not rely on the parent of the SearchView anymore. Doing so,
    the ControlPanel does not need the title attribute anymore.