Implement banning API. Adds BUKKIT-3535

This implementation of the banning API contains 2 new classes which
provide access to the internal workings of the built-in banning
system within Minecraft.

The CraftBanEntry class simply supports the representation of an internal
Minecraft BanEntry object. The data that may be modified within this new
object must be manually saved to the list contained within the
CraftBanEntry using it's save() method.

The CraftBanList class supports the representation of an internal
Minecraft BanList object through proxy methods. These methods do
validation on the passed objects where needed to ensure safe input to the
backed Minecraft objects.

These changes additionally re-route the existing banning API to the newer,
more detailed, system. Functionality prior to this change still behaves
as documented by the contract defined by the methods changed.