Tweak flags & gamemodes, add gamemode to votebook

[Pablete1234]

Adds the gamemode to the votebook hover, and refactors a few things around pgm.

• MapTags representing a gamemode now directly store a reference to the gamemode itself
• MapInfo#getGamemodes now will always be populated, if not by the map author, by tags with a gamemode.
• Implemented tab-completing for tags in /maps -t [tab] so it would now suggest wool, monument, etc.
  • Note this is affected by Fix flags not tab-completing unless string is empty Incendo/cloud#460 so tab-completion stops after you type part of the tag.