Unregister ContentObserver in InputMethodAndLanguageSettings class

A content observer (SettingsObserver) is registered when
InputMethodAndLanguageSettings is created, but it is never unregistered.

Added resume() and pause() methods to SettingsObserver inner class
to register/unregister the content observer when InputMethodAndLanguageSettings
is resumed/paused.

Change-Id: I6d4cc2625a5fd8435967d930f46e8fe86eda4714
Signed-off-by: Shuhrat Dehkanov <uzbmaster@gmail.com>