Allow generation of server pack from zip-file

1. Upload exported modpack from CurseForge app of which ServerPackCreator will then generate a server pack and allow the user to download said pack in webUI.

   1. Must be toggleable via property in serverpackcreator.properties, in case an admin who deploys the service deems it unsafe to allow strangers to upload ZIP-archives, containing gods-know what.

   2. Research posibilities of creating server packs for modpacks which aren't in the usual Overwolf/CurseForge format. Meaning: archives which do not contain an instance.json, but rather the full modpack itself, with mods and everything.

   3. If modpackDir points at a zip (CurseForge app export), install the modpack and generate a server pack from it.

Unzip archive and check contents:

if contains mods,config, assume zipped up modpack

else if contains manifest.json, assume curseforge, create modpack, create server pack

else if contains minecraftinstance.json, assume zipped up modpack, grab name, create server pack