Fracking: Missed some setPatchColor -> patchChanged changes
Fracking,Water: Well patches retain their original type

This fixes some problems in the Water model where wells were being
treated as hard boundaries -- erasing layers didn't work as expected,
and water would not flow past a well pipe within the layers.
Fracking,Water: Better handling of well lookahead types
Wells: Remove redundant WELL_IMG definition
Fracking: Fix well drawing problem where well walls/interior aren't colored properly
Wells: Add validity check
Water: Move the patch color definitions into the model
Water: Make the well head patch part of the well patches
Wells: IDs shouldn't rely on a possibly changing array length
Wells: Add ability to remove wells
Water: Remove wells if we fill in a layer on the well head, or remove the top layer under them
Water: Remove unused images
Water: Custom cursors for various editing actions
Water: Add control for removing wells