Add the ability to set ttk theme in the settings

[MOZGIII]

Currently, I have to manually alter the theme via injecting ttk::style theme use clam before color::sync_with_theme call ( a gross hack) to work around my problem with tk theming. It works though.

It would be great if I could set a theme to use via settings - git config --global gui.ttk_theme clam. I would unlock other interesting possibilities - like setting theme per repo (git config gui.ttk_theme clam) - although I'm not sure how useful that is.

[prati0100]

@MOZGIII FYI, you can take a look at this discussion to find out more ways to set the theme that does not involve editing the git-gui source.

Anyway, I think this feature is worth having. I'll see if I can find some time to implement it.

[MOZGIII]

I know of all those, and I used them before, by my problem this time is simple: macos. 😆