ecore-evas: Added support for setting/getting window auxiliary hints

ecore-evas: Added support for setting/getting window auxiliary hints

Summary:
There are no APIs for getting window auxiliary hint value which was set by a user.
Below APIs can get the window auxiliary hint value.
- ecore_evas_aux_hint_val_get
- ecore_evas_aux_hint_string_val_get

And below API can set the window auxiliary hint value by using string not id.
- ecore_evas_aux_hint_string_val_set

Test Plan: N/A

Reviewers: raster, cedric, seoz, Hermet

Reviewed By: Hermet

Subscribers: c, cedric

Differential Revision: https://phab.enlightenment.org/D2493