Make Sprinklers rust and disappear over time

[jeremyckahn]

Originally brought up in #436 by @jmmullins, Sprinklers should rust and disappear from the Field over time.

Returning Sprinklers to the Inventory should reset their lifespan.

Originally posted by @jeremyckahn in #437 (comment)

[lstebner]

i like this idea! to add to it, i think rust should only be applied after a rain, and they should still be fairly durable, but it would be nice to have a reason to replace them over time. it also might be cool to introduce a way to craft them (from mined materials) and have levels of sprinkler that are each more durable than the previous level

[jeremyckahn]

+1 to all those ideas!