Add support for uix-inputmethod apis

Add support for uix-inputmethod apis

Since the current window manager does not support converting
a normal application window into an IME window, the previous
attempt to convert an window that was created inside the
FormsApplication class into an IME window, turned out to be
an inappropriate approach.
Thus reverted "Add init interface with main_window as a parameter"
and added some interfaces to initialize and create IME window
without using ime_run main loop, and we are going to assign this
IME window as a MainWindow member variable of IMEApplication
class which is a child of FormsApplication.

Change-Id: I9d318d6ae16ba88ca808784cdddfac5f2c8043ab