Keyguard: Set WIDGET_CATEGORY_KEYGUARD when AppWidgetHostView is created

Allows the default lockscreen widget to inherit the keyguard widget
host category.  Without this, only widgets added through
KeyguardActivityLauncher are assigned the correct
OPTION_APPWIDGET_HOST_CATEGORY.

Change-Id: Ic97818d85ca5f00da0ce43bb36006d66a6935363
Keyguard: fix statusbar lags when default widget shown.

When statusbar became expanded KeyguardStatusView receives
onKeyguardVisibilityChanged callback and refreshes ClockView.
Because it receives more than one call and every time it reads
new values from resources it cause lags in opening statusbar panel.

Replace this code with BroadcastReceiver and ContentObserver to
refresh it only in case something was changed.

Change-Id: If0dbc1db059536806852661931cb2e6436f2acf4