disable dark/light stylesheet injection for custom shell themes

[AndreBClark]

• disable forced stylesheet injection if user is using custom theme to avoid overwriting custom theme css
• specifically for .cosmic-applications-dialog background color/text color
• add is_pop_theme() to check if user is using a pop theme
• fixes pop-dark overrides custom shell theme #276
  does this interfere with any other themes dependent on styles injected by is_dark()

I tested it on my local machine it appears to work.
Intended functionality:

• if user is using a custom theme prevent cosmic from injecting pop dark styling(text color/background color)

[nboumalham]

Just wasted 2 hours of my day trying to understand what on earth is happening with my sheets.

I wish I had found this merge request earlier :)

Since this merge request is soon one year old have you managed to circumvent this in any other way?

[AndreBClark]

Just wasted 2 hours of my day trying to understand what on earth is happening with my sheets.

I wish I had found this merge request earlier :)

Since this merge request is soon one year old have you managed to circumvent this in any other way?

Nope, I have not been able to find a workaround :(
I have given up trying to customize cosmic.
I suspect they won't bother updating the theming experience or even writing documentation for it until the new rust version of cosmic is released.
meanwhile I'm stuck with this ugly brown gray on several interface elements.
I have resorted to setting the super key to open the launcher instead of the cosmic applications command palette.
since I can actually access the sheets for the launcher.