Introduce Efl.Ui.Item_Container

Introduce Efl.Ui.Item_Container

this is a new widget which aims to replace Efl.Ui.Grid / Efl.Ui.List.
The widget is split up in a widget and a interface for item placement.

Efl_Ui_Item_Position_Manager: The interface contains API which is used
by the Item_Container to place the items, there is also a set of common
tests which tests for the casual tripping wires, and ensures that the
events are emitted in the correct moments (the later part still can be
improved)

Efl_Ui_Item_Container: The widget itself, it contains the API for the
enduser to add Items to the widget, it handles the different modes for
selection type and emits the events for selection changes. The pack API
is conform with the spec unit test. An additional set of tests is
defined which should be able to be run on every widget with a specific
position_manager beeing set.

Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Cedric BAIL <cedric.bail@free.fr>
Differential Revision: https://phab.enlightenment.org/D9285