got rid of a couple obsolete images

better prediction for placing horizontals at the top and bottom of the
stack, particularly if they're placed within 1 node of the correct spot.

includes just enough code to try to auto-route them as they're placed.

the "root" node is now the horizontal one - if you have diagonals and
they don't place right, they should after you dig them and place again.

nodebox for square-cornered ("large", "persian") rugs.

also added a register_on_placenode hook to make sure other stuff can be placed on top of the staircase

also make shower tray turn off taps above it, if any
minor tweak to particles function to add Y velocity
added more detailed collision boxes to the sinks to accommodate particles

so that the glass renders properly and the base appears behind it.