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.
This now splits up the rendering system into sensible parts, and makes
it easier to switch between the simple renderer and the new experimental
one. Lots of refactors I needed to do for a while are now done, too.
