Try to restore inventories on server join.

This should have absolutely no effect due to the implementation
of the restore method. If no file exists, nothing happens, but if
for some reason the inventory was never restored, it will be.
Add support for class item chests.

This is an extremely ugly, hacky way to do it, but the feature
should definitely make it into 1.0 - it requires no commands or
any other complex setting up besides flipping one option in the
config-file.

Upon clicking a class sign in the lobby, MobArena will (if the
config-setting is true) search for chests below the sign, and
below (and including) the block behind the sign, i.e. the block
that a wall sign would be attached to. If a chest is found, the
contents will become the class inventory.

The search can be optimized to be a one-off thing unless the
block changes from being a chest. A todo for 1.0, perhaps.
Make the chest search happen per-pillar.

This allows for a sneaky little trick, where two lines class signs
becomes possible, if one chest is offset backwards, and the other
chest is positioned at the very bottom block.
Fix possible NPE.
Swap order for vertical layouts.
Fix possible NPEs.