Fix touch accessibility in keyguard.

This changes the accessibility code to monitor state changes
and replace the touch listeners with click listeners when
touch exploration is enabled.

It also fixes a bug where the first touch on the camera was being
ignored by ensuring KeyguardTouchDelegate has started the service
by the time the button is touched.

Bug 10991981

Change-Id: I7c4bf01f9bfa10f54cadb0809b6af526c5386af5