Settings: Let users disable the left-corner Keyguard widget

The application widget is a generic icon displayed on the lock screen
that allows a user to launch an activity.  This is part of the Appcast
flow.

Note: The intents necessary to manage this widget is protected by a
system|signature permission.

Change-Id: Ida245b8c096a24ca3d8bb9a09c6af383bf3295cf
Reviewed-on: https://gerrit.nextbit.com:8443/8255
Reviewed-by: chub <chub+gerrit@nextbit.com>
Tested-by: chub <chub+gerrit@nextbit.com>
Settings: ButtonSettings: Introduce recents long press action

Add a new preference in Settings > Buttons > Recents long press action
that controls the behavior of recents long press intent
ACTION_RECENTS_LONG_PRESS.

The user preference is saved in
Settings.Secure.RECENTS_LONG_PRESS_ACTIVITY; if empty the default is the
system's "switch to last app" behavior. Settings.Secure is used
intentionally over Settings.System for permission reasons.

Change-Id: Ifc61b5958a88360e32db31459f0205b6ba5306b3
Merge remote-tracking branch 'cyan/cm-11.0' into cm-11.0