Huge update to the GUI codebase.

- Make match screen in gui-desktop non-singleton, allowing multiple games to be played simultaneously.
- Separate global gui commands (IGuiBase) from game-specific gui commands (IGuiGame), allowing games to send their commands to the correct gui.

forge-core/src/main/java/forge/card/mana/ManaCostShard.java

@@ -22,7 +22,7 @@ import forge.util.BinaryUtil;
 /**
  * The Class CardManaCostShard.
  */
-public enum ManaCostShard implements Comparable<ManaCostShard> {
+public enum ManaCostShard {
     // declaration order matters! Place the shards that offer least ways to be paid for first
 
     /* Pure colors */