This takes the existing properties widget in the new material editor and
makes it reusable across multiple applications. It's now added to the
Armoury which shows the gear's used materials. It's also added to the
Data Explorer which now supports viewing material files.
I fixed the render viewport crashing when hiding it again, and made it
even more resilient.
Adds basic glTF import (although right now it only imports back
positions) and fixes support for more of the vertex data that's
available to us. The MDL file isn't written back out yet either, it only
displays in the viewport.
