[WIP] Made gamemodes per player

[PureTryOut]

This PR is making creative-mode entirely per player (where it's per world right now), so on servers individual people can become creative or survival mode instead of all of them. Where possible I'm trying to make it gamemode "independent". Meaning it can later be extended to support adventure and spectator mode as well.

Things to do:

• [x] Add command to switch between gamemodes
• [x] Making inventories per player
• [x] Enable/disable hud per player
• [ ] Enable/disable damager per player (also ignore the current enable_damage setting) (as of yet impossible)
• [ ] Allow per player creative block breaking
  • [x] Bare hand
  • [ ] With tools and/or items in the hand (as of yet impossible)