Fix 5231823: PIN/Password polish on lock screen

Fixes these issues:
- add IME button to switch IMEs on password screen on tablet
- centers '0' on PIN screen for phones and tablets
- tablets now use the same ICS background key asset as phones
- make PIN layout consistent between phones and tablet
- center the I-beam when any button is showing in the password entry field

Change-Id: I4da0173f9b2efeab46617c5a41a8132895b63a97