elc_popup: add escape key binding

elc_popup: add escape key binding

Summary:
There are no methods to close the popup with key down.
So I added the escape key binding to close the popup with escape key.

Test Plan:
1. patch this code
2. delete /home/{user}/.elementary to refresh the config value
3. launch elementary_test -to "popup"
4. click one example of the list and press escape key
5. see closing the popup

Reviewers: cedric, raster, jpeg, Jaehyun_Cho, Hermet

Reviewed By: Hermet

Differential Revision: https://phab.enlightenment.org/D3876

Conflicts:
	src/lib/elementary/elm_priv.h