elementary: Focus improvement for elm_genlist and elm_list

elementary: Focus improvement for elm_genlist and elm_list

Summary:
This patch applies automatic focus feature to elm_genlist and elm_list
containers.
Currently (prior to this patch), focusable widgets inside list items of both
containers receive focus by an explicit mouse click over them, and lose focus
when focus goes to someone else in the window.
This change also adds the ability to:
- focus by default on the first-from-right focusable widget upon items selection
- lose the focus when another item is selected (focused or not)
- move focus between focusable widgets inside the same item by left and right
arrow keys accordingly (up and down keys when elm_list is in horizontal mode)

Focus is supported for horizontal and vertical lists.

Tests have been added for genlists and lists to check focus feature.