Update keyguard to send userActivity events

Since the new PowerManager changes are in, keyguard needs to handle
keeping the screen awake.  This change does this in a few places in
addition to the existing security screens:

- when the widget page changes
- when the user interacts with any widget other than the status widget
- when the user taps on the target in the selector screen

Fixes bug 7273646

Change-Id: If4c76a38e9b886dd359ba96cd2aae03652007b66