zoning UI cleanup part 1

[PeenScreeker]

This pull request implements several changes being tracked here:
momentum-mod/game#2122

This can likely be reviewed by changes rather than by commit, but the history is preserved in case reviewers would like to see how this PR relates to the checklists in issue 2122.

REQUIRES SIMULTANEOUS RED CHANGES

Main changes:

• Only allow zoning UI to be opened when sv_cheats is enabled
• Styling improvements to tab menu related to zoning (hide header, padding, footer contents)
• Zoning UI styling improvements (bg colors, padding, indentation)
• Reworked add/delete functionality
  • Buttons inline within tracklist tree
  • Add buttons no longer selection dependent (add checkpoint to arbitrary segment)
• UX improvement for placing corners, set zone height
• Better communication between UI and engine for point placement state

Checks

• I have thoroughly tested all of the code I have modified/added/removed to ensure something else did not break
• I have followed semantic commit messages e.g. feat: Add foo, chore: Update bar, etc...
• My branch has a clear history of changes that can be easy to follow when being reviewed commit-by-commit
• My branch is functionally complete; the only changes to be done will be those potentially requested in code review
• All changes requested in review have been fixuped into my original commits.
• Fully tokenized all my strings (no hardcoded English strings!!) and supplied bulk JSON strings below

[tsa96]

Are you sure you're trying to merge into the correct branch?

[tsa96]

This PR still seems wrong, I think you're targeting the wrong branch!

[tsa96]

Only spotted one issue, rest is good. Big fan of how simple you've kept everything, super readable code.

[tsa96]

Okay LGTM

[tsa96]

Yup still looks good