More Active display fixes

PS1: re-enable proximity activated screen-off when Active D is showing only
PS2: add broadcast intent to notify active D when keyguard unlocks
PS3: completely disable proximity mode when the user unlocks the device
     either from active display or from the keyguard.  The sensor is still
     active on the keyguard if the user manually powers on but it's much
     better than it was before

Change-Id: Ie4da497eaca75056d5e7ba337f6aba0cde8ea5e4