Simplify the architecture a bit

* Merged BetterEnderIOLogic into BetterEnderFileHandler.
* Removed all setters from the BetterEnderChest interface.
Initial version of flatfile name --> UUID conversion
Fix ChestOwners.fromInput throwing IllegalArgumentException
Refactor UUID conversion code a bit

This prepares ourselves for the MySQL database conversion.
Initial version of MySQL name --> UUID conversion

When the UUID is not found, the chest is simply dropped at the moment.