Update v1.15b

Change Logs

--- Pull request changes ---

- Added configurable prepare time
- Added a Hardcore mode option (Disables respawning)
- Added an option to allow players to join mid round (Disabled by
default, enable it in the config)

- Fixed the double points bug

- Added configurable powerups

- Fixed a spelling error
- Moved the text of the round higher

------------------------------

- Added Physgun to the create mode.
- Changed the way the gamemode saves the random box spawns & perk
machine spawns. (For Physgun)
- Added the easter egg tool (Allows you to add small easter eggs to your
maps)
- Changed some default values
- Added 2 chat commands to generate a nav mesh
Merge branch 'master' of https://github.com/Alig96/nzombies