Theme Rework

[DarkRTA]

1.2.0 is planned have a complete overhaul of how themes work to reduce jank and take advantage of our new knowledge.

General ideas:

• Expose unset as a theming option which instructs rb3dx to not set a texture at all.
• Allow recoloring as much as possible
• We should probably use the vanilla shading by default and only set emissives where needed.
• Allow per track instrument selection.
• Clean up how we set textures.
• Ship some default themes as this new system is likely to be extremely in depth.

A lot of discussion for how this stuff will even work should take place here before we go and implement it.

[jnackmclain]

For sure agree. I have a couple ideas I had potentially for overshell in the new rework. One would be to group items together a bit.

Say, "Highway" as a top level category, containing highway, streak, overdrive, beatlines, etc. To keep the top level less complex for the user.

Another idea potentially is to try and take advantage of customizer more directly. Similar to how yarg gives a track preview, perhaps we should load customizer when entering the texture menu automatically to allow for a more visual "menu" for setting up your theme.

And in that vein, we could even potentially try and take advantage of the cancelled dx settings rework as the navigational screen for customizer, instead of using overshell.

[DarkRTA]

Moving theme settings out of overshell and into this new menu is probably a good call.

There's gonna be a lot more options and if we do it all in overshell, its gonna get a bit cramped.