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

for the system clock widget this does not make much sense but due
that our system default is DashClock it makes a lot sense to
allow it to see more content of DashClock extensions

So allow it for overlay added app widgets if the binding was
sucessfull.

Change-Id: I0365573c6fa88117a47b01ced81eb36f75324342
fb: Keyguard disable challenge drag down on slimpin/simpuk screen

On simpin, simpuck and as well account change screen it does not make
any sense to give the user the abillity to drag down the challenge to show
the widget maximized (neither if widgets are enabled or disabled)
Reason: simpin/simpuck widget is not shown due of security reasons
and on account change the next expected behaviour is that the user gets a new
setup. So it does not make in this case as well sense

Just check for current securityscreen selection to block this behaviour. As
well move the enable/disable code to a proper place

Change-Id: I0b16d1e590252b537d6c71c4aa9b133ed832be45
Keyguard: Ensure that a widget and page is attached before attaching the ChallengeLayout.OnBouncerStateChangedListener

otherwise it can result in a NPE due that the page was not loaded. Especially on low end
devices this can happen (see zoomOutToBouncer() method @KeyguardWidgetPager)

Change-Id: I7e940eb2fdf885f158f4c5ff2872ebafcda76da0