OpenLock Cavern River (Thin)

Based on the previous river cavern design (Matt Crott remix), but with the river bed at only 5 mm height. This requires creating a thinner 2mm OpenLock clip (included) to attach to other tiles since the tiles are not as thick in the center, so they are somewhat OpenLock compatible using the thin clip. The river banks are at roughly 9 mm height but with some variance.