Tablets now consume energy.
Cleaned up and stabilized tablets some more.
Tablets now do *not* keep running across saves (unload/reload). This was causing too many issues when they were left in running state in inventories / lying around, and would have failed anyway if the world was saved while the owning player was not in the game (which happens all the time on servers, after all).
Added one-slot inventory to charger, can be used to charge tablets.