Keyguard: let the user drag the challenge down if widgets are disabled

for the system clock widget this does not make much sense
but since our system default is cLock it makes sense to
allow it to see more content.

Change-Id: I0365573c6fa88117a47b01ced81eb36f75324342
Merge "Keyguard: let the user drag the challenge down if widgets are disabled" into kitkat-caf