Save game scores to an SQLite database. [Incomplete!]

Implemented basic features (mostly stable).  The remaining features are mostly graphical.
- Added package org.xerial.sqlite-jdbc.  All scores are saved to .opsu_scores.db on table `scores` after a game completes.
- Added "Scores" class to handle all game score data (including database connections).  The "Score" subclass encapsulates all database fields.
- Added "score viewing" constructor to GameData, for use only in the ranking screen.
- Draw the grade of the highest score next to expanded song buttons in the song menu.
- Added "bit" and "abbrev" fields to GameMod, used in storing/displaying scores.
- Hide the retry/exit buttons in the ranking screen when viewing a score.

Other changes:
- Removed "objectCount" field in GameData (no longer necessary).
- Removed "getID()" method in GameMod (no longer used).
- Moved most drawing in GameRanking state to GameData.
- Removed File parameter of "GameData.loadImages()" (leftover, no longer used).

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

.gitignore

@@ -5,6 +5,7 @@
 /Songs/
 /.opsu.log
 /.opsu.cfg
+/.opsu_scores.db
 
 # Eclipse
 /.settings/