Implemented remote console (rcon) support (closes #451).
Added support for player and mob heads.

Includes dandling for the skull item, block, and tile entity, as well as
lookup of profiles based on username for Bukkit support.
Implemented wall and standing banners.

Covers placement, tile entities, serialization, and sending the banners to
the client. Does not include crafting.
Merge branch 'master' into pr-272