Better Mop and Cart love

Slight tweak to the behavior of attacking the janicart with a mop.
Changed it so that it tries to soak the mop then stores it, as I'm sure most players would prefer their mop to always be fully soaked when they remove it from the cart.

Also changed the examine text from 'water' to 'liquid' as it was misleading. 
It can actually be filled with any reagent, even welder fuel...or acid... or blood... or dr.gibb...space lube... you get the picture.