Make keyboard show up automatically in the passphrase prompt activity

It is really annoying that the user has to touch the text input, each time he wants to unlock the application. In order to speed this use case up, I propose that the keyboard is automatically shown, since the only action that is done on this activity is to type in the passphrase and hit the unlock button. Additionally I replaced the 'Next' button by one, labeled 'Done'. It shares the action with the 'unlock' button.