WIP on annotation helper to PreferenceActivity and PreferenceFragment

This PR is a WIP, and related to #7.

I decided to use resource IDs instead of plain string preference keys in the annotations, since this is the suggested way (if you use a string resource as a key, you can use it both  in java and xml).

The implementation is basically the same as View injection/listener. Currently there is some code duplication, but i am not sure we should remove that, because it would really obfuscate the intent of the code.

@yDelouis, @DayS, @dodgex i appreciate your feedback.