Implements #13 and #14

Removes deaths and time as separate game-modes, and instead always tracks records.
Adds two proper game-modes. One inverts the player's controls, and the other randomly inverts the player's controls every 7 seconds.
Saves cleared status and records for each game-mode separately
Only allows 0-1 for the horizontal velocity
Requires arenas in arena groups to be cleared in sequence on all game-modes, not just the default one.

src/main/resources/plugin.yml

@@ -24,8 +24,8 @@ commands:
     usage: |
       /<command> <arena> [mode]
       Mode can be used to select challenge modes which can be played after beating the arena.
-      deaths = A least-deaths competitive game-mode
-      time = A shortest-time competitive game-mode
+      inverted = A game-mode where the WASD buttons are inverted
+      random = A game-mode where the WASD buttons toggle between being inverted and not
     description: Used to join a dropper arena
   dropperleave:
     aliases: