Added login activity strings to their own file. Renamed assets to better specify their use.
Changed login activity to be the main one and added main activity as a secondary one.
Did a bit of cleaning up:
* refactored the code so that it matches the rest of the projects *please read Code Style*
* removed the useless fragment from the login activity; there's simply no use for it here
* added login functionality to the button through a listener
* changed layout ids to specifically tell that they're in an activity (just login is too ambiguous)
* added and id to every view in the layouts