Attempt to fix #261 and fix #163
Added HUD layout updates on status bar visibility change.
Created a class to encapsulate highlighter and HUD.
Encapsulated highlighter and HUD in TeclaVisualOverlay class.
Set background resource to normal switch screen on long click.
Removed all unused click listeners in SingleSwitchTouchInterface and TeclaHUDOverlay.
Processed switch events on switch released.
Added a line to update switch pressed state.
Updated scanning settings in persistence when checkbox preferences are changed.
Set preference change listener for the scanning settings checkboxes.
Integrating scanning settings preferences to the app.
Merge branch 'issue-238' into issue-295
Merge branch 'issue-294' into issue-295
Implemented inverse scanning.
Corrected code for handling switch release events.
Merge branch 'issue-294' into issue-295

Conflicts:
	package/tecla/addon/TeclaAccessibilityService.java
Added missing line back to handleSwitchEvent method.
Updated preferences on resume of setting activity.
Set self scanning when inverse scanning is changed.
Stopped keyboard from self-scanning when HUD is disabled.