Add new setResourcePack method. Fixes BUKKIT-5015

Minecraft now uses resource packs instead of texture packs, which broke
the setTexturePack method, as the client no longer listens on the MC|TPack
channel.

This commit fixes the issue by adding in a setResourcePack method, and by
deprecating setTexturePack and rewriting it to call the newly added
setResourcePack.  In order to simplify the method and prevent this from
happening in the future, setResourcePack calls EntityPlayer.a(String) to use
the same logic as minecraft when sending resource packs.