Colorselector: Item_signal_emit_hook added.

Colorselector: Item_signal_emit_hook added.

Summary:
Issue: If application has to preselect an item, or change item properties by customizing theme
there is no option provided for the same.
Solution: Add item_signal_emit_hook.
Signed-off by: Shilpa Singh <shilpa.singh@samsung.com>

Test Plan:
Send a signal to item and verify UI
Elm_Object_Item *item = elm_colorselector_palette_color_add(cs, 133, 100, 255, 255);
elm_object_item_signal_emit(item, "elm,state,selected", "elm");

Reviewers: seoz, Hermet

Reviewed By: seoz

CC: govi
Differential Revision: https://phab.enlightenment.org/D504