Support starting KPD with a password and immediate-launch flag

This adds support for two new keywords for KeePassDroid's password activity when started via intent:

- Password: supplies a password for the database
- Launch immediately: immediately attempts to decrypt the database with the supplied password (and, optionally, keyfile).

I wrote this support for KeePassNFC (http://code.lardcave.net/entries/2013/04/01/215058/) but I think it's a generally useful thing to do. 

I hope you can accept it as-is, but I'd be happy to make any changes you suggest.