Added locale support for gm command

[Pathaleon]

Message returned on use of the gm command did not previously support the
localization file.

[wizjany]

tr("gameModeCommands.switch", GameType.getById(mode))

...

gameModeCommands.switch=§eYou have switched to {0} mode.

edit: while you're at it, there's an extra newline on line 40

[Pathaleon]

Ah so that's how you include the variables. I guessed it was but I wasn't aware how to use in the module side.