UI needs more polish

[Kriper1111]

The limits planes should be semitransparent and striped (maybe via built-in GL_BLEND, or by depth-sorting them). With different colors by normal (via gl_FrontFacing mix).

The acceptable range should have a decent outline and be shaded (probably matcapped).

UI itself will need some polish work, details are yet to come from designers. Probably include shader color picker for final builds.

[Kriper1111]

This issue is being addressed in ui-glowup branch, which will be merged after framework-fix gets some updates, and merged into main branch.

[Kriper1111]

In other updates, there are now:

• AVR edges "wireframe"
• Custom colors
• Optimal plan vector (primitive, will have to get more attention)
• Better grid and zoom (-ish)

We'll consider rearranging the UI around in further commits, but for now we have to:

• Finalize localization (few issues there)
• Update vector displays (and add objective function too)
• Add ability to select constraint type
• Re-label math terms to proper ones (e.g. all occurrences of "target function" to "objective function", etc)

Bit later I'll open a PR, which is based
..off of this issue.

[Kriper1111]

Now being a candidate for merge in #15