Added income frequency

- Added years and quarters to the interface
- Created timer that increments the number of quarters in a year until it reaches four. After four, the quarter resets and the year increments.
- Renamed TowerData to GameData

project/src/autoload/gamedata.gd

@@ -0,0 +1,8 @@
+extends Node
+
+var tower_name: String
+var budget: int = 2000000
+var year: int = 1
+var prev_quarter: int
+var quarter: int = 1
+enum GameSpeed { SLOW, MEDIUM, FAST }