Add current version of water model
Model optimizations

@refreshPatches = false causes AgentScript to not redraw the patches on
every tick.
Water model: Default to the next patch being downward
Water: Water creation tweaks

Stop after 4000 droplets (it gets wonky after that).
Ensure we never create 2 on the same starting patch.
Bump agentscript version
Water: handle null when checking patch occupation
Add water model to index page