GamemodeOverhaul

Restores removed command arguments, and adds a few shorthand commands.

Added commands (all configurable):

• /gamemode 0/1/2/3/s/c/a/sp
• /gm (shorthand of /gamemode)
• /defaultgamemode
• /dgm (shorthand of /defaultgamemode)
• /difficulty 0/1/2/3
• /toggledownfall