Add comparator. Add sorts

Needs working on the comparation, they are still naked.

Also needs to correctly build the student object.
Add sorting. Fix preferences.

Added sorting for the record. Now the preference actually works and the record is reordered on the fly.

TODO: On-the-fly reordering without entering preferences (should be really easy to get).
Separate strings.xml

Separated strings.xml into different files for better tracking of the strings and translation.
Add demodata.

Added string with demo data.
Fixed rotation.

Rotation is now fixed, shows the proper information in the proper places and keeps the state.
Fix sorting + rotation. Add stub for language.

Added stub for language change. Fixed sorting and rotation. Fixed preferences screen (now shows as summary the selected option.
Changed parameters to match strings*.xml files instead of hardcoded constants.

Fixed crash upon recreation of activity when one of the latest grades was chosen.