Adjusted break mod and locks

1. I updated some of the multi-break mod code today, to have it keyed off of the general material model that the lug/weight mechanics are based on. This means that lockables are more durable, as are "construction materials"; this includes wooden planks.  That means planks' weight has gone up a bit, but now they provide much more protection than before (they were only 1-break before).
2. Locks now properly destroy when the block holding them is destroyed.  Before breaking a locked chest and then placing a new chest in the same location would inherit the same lock.  Now that's no longer true (the lock is tethered to the specific block in the spot).