genlist: Add item loop feature

genlist: Add item loop feature

Summary:
If item loop feature is enabled, item is moved infinitely.

    1. Refactor direction key event handling routine
      - added internal function _elm_genlist_elm_widget_event_direction.
    2. Add looping feature for genlist
      - added Eolian function _elm_genlist_elm_widget_item_loop_enabled_set/get.
    3. Add demo - test_genlist.c / genlist focus

Reviewers: seoz, woohyun, jaehwan, Hermet, raster

Reviewed By: Hermet

Differential Revision: https://phab.enlightenment.org/D778

Conflicts:

	src/lib/elm_widget_genlist.h