Add safe methods from @md-5's offlineUtil.

Adds in the safe (well, safer) methods of @md-5's offlineUtil branch of CraftBukkit-Bleeding. These methods read information about a player from the offline records. OfflinePlayer does not have an associated datawatcher, so if the player logs in while a copy of the corresponding OfflinePlayer is held, the data is no longer expected to be correct (though it should still be safe).

Thrown out were the set and write methods of this util, since there seems to be a poor understanding of what should and would happen if these methods were called in the same tick that a player logs in (since OfflinePlayer does no promotion to Player). For that reason, those methods are considered to be unsafe, and were discarded.