Fix keybinding conflicts on 1.14+ (fixes #268)

This fixes both, replay-exclusive keybindings blocking vanilla ones as well as
vanilla keybindings blocking replay-exclusive ones.

The magic happens in Mixin_ContextualKeyBindings.

src/main/java/com/replaymod/replay/ReplayHandler.java

@@ -237,7 +237,7 @@ public class ReplayHandler {
         //#endif
         overlay.setVisible(false);
 
-        ReplayModReplay.instance.replayHandler = null;
+        ReplayModReplay.instance.forcefullyStopReplay();
 
         mc.openScreen(null);