Less fat zombies
In the advanced inventory, recognize when the player is not grabbing anything.

This is particularly troublesome in the following scenario:
* grab something (a shopping cart)
* Enter AIM
* Assign a pane to be [D]
* Exit the AIM
* Release the cart
* Enter AIM
* You can't easily switch slot on the pane assigned to be the [D]
Adds a vehicle-mounted water faucet.

Copies existing functionality from the RV kitchen unit to allow the
player to directly access a vehicle's water tank and have a drink or
fill a container with clean water. Useful for small vehicles, since
siphoning water with a rubber hose takes close to half an hour
currently.
The water faucet will semi-rarely spawn in public works and sewage
treatment plants, and is craftable with Fabrication 1 and Mechanics 1.
As well, I've edited the RV kitchen unit recipe to use one water faucet.

Note that even though this is a pretty simple addition, this is babby's
first PR, I would appreciate if it was double-checked to see that I
didn't screw something up!
Merge branch 'faucet' of https://github.com/9600bauds/Cataclysm-DDA into 9600bauds-faucet
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA
Merge Adv inventory pane management fix.
Merge reduction in spawn rate for fat zombies.