Fix gesture preview image visibility not set correctly.

- update for the preview image is done only in onStart()/Stop().
Move the handling to onPause()/onResume() instead so that visibility
updates will also be done when switching between pages.
- remove the obsolete GesturePreference class.

Change-Id: I743a9d41f17aab3303201e11e5bba708ca5810ae
Fix: 63783217
Test: make RunSettingsRoboTests