Nicer dark mode visuals

[adamchalmers]

@nicboone8 showed off some parts in a nice color scheme and asks us to "shift the default dark theme colorway to lighter surfaces with darker edges". For example, see these screenshots from Rhino7, (viewer = "Arctic", shadows on, surface edges visible)

@franknoirot says the frontend can get a lot of the way there currently, but @mlfarrell says he wants to add some things to the engine to make it really pop, e.g. changing SSAO radius, increasing sample counts.

[nicboone8]

I started thinking about color scheme because the bright white edges + darker surfaces combo currently used in the modeling app sometimes throws me off a bit. Parts don't quite feel like real parts. I tend to stick to the light theme for that reason, despite a general preference for dark mode.

Obviously not urgent at all - just something I was noodling over!