Per plugin resource-packs

[yusshu]

At the moment, plugins have to listen to the ResourcePackGenerateEvent and register their resources in the single, server resource-pack initially created by creative-central.

This new idea of per-plugin-resourcepacks would be similar to how external resource packs (e.g. from ModelEngine4, ItemsAdder, Oraxen) are currently handled in the Bukkit plugin. The external resource pack provider loads the resource-pack and it's then merged with the central resource-pack.

For example:

interface ResourcePackProvider {
  String pluginName();

  ResourcePack create();
}

We could have something similar for creative-central plugins, which would allow:

• Check the amount of resources a plugin generates (we could have something like /central info <pluginName>)
• Check which plugins are not compatible with other plugins

This will also remove the need of 'ExternalResourcePackProvider's, since they can be normal ResourcePack providers, but registered by creative-central.