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). Also the implementation is easier, since we can rely on existing concepts.

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. But i gladly accept suggestions on that.

@yDelouis, @DayS, @dodgex i would appreciate your feedback.
just a note that we keep in mind to update the wiki https://github.com/excilys/androidannotations/issues/1157