Added the initial mod skeleton!

Devlog #1 of Sponsor System mod
Soo since this is the first devlog I basically spent time setting up this project, setting up the github repo, etc.
Outside the boring set-up stuff though I added the core skeleton of the mod, thus there’s now a command to invite a player. If you have not been invited to the server, you cannot join, since by inviting someone that player is added to the server whitelist. Now funny enough this actually kinda screwed me over during testing, since I was the first player to join, nobody has invited me yet. And since I suck with adding whitelist entries, I was prohibited from joining the server. But not to worry, I’ll be fixing this next time (hopefully).