Implement Render Subpass Chunking

Write some optimizations that allow for subpass chunking - i.e. to divide the render area into smaller, more manageable chunks and render those.

This has two parts, firstly we need to determine where our regions are. Next, we'll assign shapes/compartments to each region based on their bounding boxes. We will need to tag each shape that should be put into each region (note that some shapes will be in multiple regions since they could be half in one and half in another. (Note that this would also be a great part to split across nodes, each node could render one region at a time).

Then, we just enumerate each of the scan regions, rendering each one until the whole area is done.