clock: Add elm_clock_pause_set and elm_clock_pause_get functions for elm_clock widget

clock: Add elm_clock_pause_set and elm_clock_pause_get functions for elm_clock widget

Summary: This patch add two functions for elm_clock widget - elm_clock_pause_set and elm_clock_pause_get. I've prepared it because I want to do a stopwatch using this widget, but now it is impossible to pause the clock without set an editable mode.

Reviewers: seoz, cedric, stanluk, z.kosinski

Reviewed By: seoz

Differential Revision: https://phab.enlightenment.org/D374