Make Crates constructable, and sealable

So, if this gets merged, you will be able to construct crates, like the ones occasionally found scattered on the countryside.
Also, you will be able to seal (any) crates. This might be useful if you want to lock your stuff away, so that no sneaky NPC may take it. (Not sure if they won't just smash it, btw.)

Tell me, if the numbers need some changes.
>I'd be OK with only requiring nails.

Seconded.