Blender Git Loki

* Removed the grey overlapping 'region manipulation' triangles.

- They were causing unnecessary visual noise, breaking up the lines of the region edges
- Now you can just drag anywhere on a region edge to resize it, like existing area edges
- To minimise a region, click once on the region edge, or resize it down to nothing. For minimised regions, a (+) icon will appear, which you can click to restore it to the size it was before it was minimised.