add ctfd-modules

[caprinux]

CTFd modules is a plugin that further categorizes challenges into modules. The main purpose of this is to better organize challenges which would be useful when CTFd is used as a training platform.

Hi CTFd team,

I'm submitting this PR to add a new CTFd plugin to categorize challenges into different modules.

This will be useful when CTFd is used as a training platforms as we can segregate challenges into modules and within each modules, have different topics (as categories).