4931 skin frame colors

[egmontkob]

Proposed changes

• Use more consistent internal constant names for colors
• New skin colors for frames
• sand256 skin: Use non-italic frame characters

• Resolves: Skin: separate colors for frames #4931

Checklist

👉 Our coding style can be found here: https://midnight-commander.org/coding-style/ 👈

• I have referenced the issue(s) resolved by this PR (if any)
• I have signed-off my contribution with git commit --amend -s
• Lint and unit tests pass locally with my changes (make indent && make check)
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation (if appropriate)

[egmontkob]

Here's the makeshift script I used to update the skin files: mc-4931-update-skins.sh

[egmontkob]

Since the PR does not alter the look of any of the skins (except for that tiny italic fix), you'd have to create your own skin to test the change. Something like replacing all *frame = * with *frame = brightcyan; for testing purposes.

[egmontkob]

frame.ini.txt

Here's a slight variation of the default skin, using differently colored frames.

Place in ~/.local/share/mc/skins/frame.ini (remove the .txt extension) and launch mc -S frame.

It's for demo purposes only, I don't mean to include this in mc, but hopefully some cool skins using this feature will emerge soon.