Keyguard: bring back longpress unlock

This will readd the possibility to unlock the device by
longpressing the lock icon when widgets are maximized.

Change-Id: I8dba1ed49a4731ba388ab9ee050cf56925d678a0
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Merge "Keyguard: bring back longpress unlock" into kitkat-caf