Ability to select individual triangles, for debugging purposes

[Robert Jordan]

When debugging meshes, there are times where I want to select an individual triangle and see its properties or change it in some way. Putting each triangle in the tree view would probably be overkill, but the ability to select them in the render view would be useful.

A selected triangle would ideally show an outline around its perimeter, making it easy to identify, where as a bounding box would be more difficult to pinpoint what was selected.