Add timer for callbacks in main loop

Add timer for callbacks in main loop

- Issue:
When the app calls setting API in sub-thread, the changed callback can
not be invoked properly.

- Solution:
Most ecore API function properly works in main loop, and
ecore_timer_add() is also a functions of this kind. Therefore, if the app
calls setting API function in sub-thread, the changed event callbacks
can not be invoked. To solve this issue, this patch changes the ecore
timer registration logic. Through this patch, every timer will be added
in main loop by ecore_main_loop_thread_safe_call_sync().

Change-Id: I8ce976cf2b86b1c2a309ea887f17f1641b9e3f01
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>