Implement delegate-based pin validation

Fixes #18
Validation is now performed by the delegate, rather than the padlock
controller itself.
Support complex pincodes with unknown length + more

Implements issue #17

Complex pincodes now show a text field with dots, so any length
pincodes are supported and pin code length is not required to open the
padlock view. Complex pin code displays an OK button (after at least 1
character).

Additional improvements:
iPad fixes, text localization, more iOS7.1 look, fixed some typos