Move CTFd theme to seperate repository

[The0mikkel]

Currently, the core-kubectf (KubeCTF Theme) is located withinthe themes directory.

It should be moved to its own repository, to serve as a template.

Tasks

• Move theme to new repository
  • Create new theme repository
  • Create submodule link in ctfpilot/ctfd
• Document theme with origin and changes for KubeCTF