optional encryption password sync

Option to use 2 different tokens for encryption and locking.
Allows convenient usage and strong encryption at the same time.

Inspired by reading next:
https://santoku-linux.com/howto/mobile-forensics/how-to-brute-force-android-encryption

Related discussion:
http://code.google.com/p/android/issues/detail?id=29468

Change-Id: I66dd920b120c6964fa1b3786cd13ea32cf663893