LockScreenActivity
Move ImpsProvider to remote process

allows UI process to be reaped by OS
fixes issue #1910
close sliding menu with back button
fix DB creation with passphrase

also, always finish WelcomeActivity so user can't back into it
fix empty password handling
fail fast on failure to initialize OTR

OTR is not optional.  Failure to initialize OTR makes incoming messages drop on the floor.

This could happen if the OTR keystore is corrupt, the password is incorrect or there is a bug
in order of initialization.  I suspect the latter in a failure case I saw with one of my testers.
Work around bug in CrossProcessCursorWrapper and 1MB limit
Merge pull request #280 from devrandom/mem

Improve memory behavior