Add event for providing Resource Packs

[DasEtwas]

What are you suggesting? When connecting, the server will currently send the same exact list of resource packs to every player.

An event should be triggered instead, acting as a sort of "resource packs request" to event listeners. The server then implements the same logic as before but now in an event listener fashion. Plugins could then intercept this event to provide custom resource packs. Because RP download is a data stream, user code should be able to supply an InputStream.

Also, this would make RP debugging easier by e.g. changing pack version numbers before downloading, causing client-side RP cache misses and redownload of development packs.