Use default encryption password if an accessibility service is enabled.

If accessibility is on and the user selectes a secure lock we use weaker
encryption to enable running accessibility layer at the time the user
authenticates. This change adds a warning message to the enable accessibility
service dialog if there is a secure lock and also adds a warning as a
summary for the secure lock in the lock chooser activity. Both warning
mention the weaker encryption to be used.

bug:17671790

Change-Id: Ib5cc9d3a78f751e18362bb9238fd2804c3b600f8