Resource pack events

[TheEpicBlock]

Ideas:

• [ ] Event when resource pack is finished
• [ ] Event for when advanced resource pack maker is copying into the temp location
• [ ] Maybe replace PolyMcEntrypoint#registerModSpecificResources with an event?
• [ ] Event for when PolyMc is looking for a file, allowing you to give a location for that file?

Especially the first one would be useful for mods that need to manage resource packs in some way. Uploading it to a server for example.