Add read/write permissions to access the external storage unit of the
device
Fix crash when trying to access savefiles.
Make SaveGameActivity finish when it chooses a new file.
Remove unneeded libraries
Refactor difficulty strings so that they match the constants in the
Difficulty class and match the standard, Easy-Normal-Hard categories.
Add savefile to the class to hold the save file name for ingame saving.
modify the constructor to support savefile.
Document class.
Refactor adapter so that it filters out unreadable, incompatible,
unrelated and/or corrupted files. The code is also sturdier than before.
Refactor code so that it uses the new GameDetails constructor.
Create OnSaveSelectListener so that the SaveFileChooserFragment can
callback on its parent when the user chooses an item from its list. Also
applied the interface to the SaveFileManagerActivity (turning it an
abstract class) so that it can be used by the load/save screens.
Define OnListItemClick method to call OnSaveSelectListener callback.
Implement OnSaveSelect Listener on both classes effectively completing
their functionality.