Many bug fixes.

Removed some unnecessary debug output.
Fixed check if entity is dead.
Fixed GUI not going away when battle is over.
Fixed creeper explosions not doing damage.
Fixed mob attack phase where mob target is null.
Fixed mob not attacking anymore after one turn.
Fixed null pointer in handling Battle info query (when battle has already been ended and has been removed).
Reduced sleep time for battle updater thread to 500 milliseconds.
Cleaned up references to client side Gui.
Removed button to unimplemented "Change Weapon" action (temporarily).
Removed unused class "EntityInfo".