PICARD-1377: New plugin UI icons

[phw]

Summary

• This is a…
  • Bug fix
  • Feature addition
  • Refactoring
  • Minor / simple change (like a typo)
  • Other
• Describe this change in 1-2 sentences:

Problem

• JIRA ticket (optional): PICARD-1377

Use the new icons designed by @Aerozol for the plugin UI.

Solution

Set the icons. Also add dark UI detection and use a separate set of icons.

Action

@Aerozol The plugins looks really clean and good. But I think the trash can is a bit small, what do you think? Shall we make that a bit larger?

[rdswift]

Once this is implemented, we need to update the images in the documentation at https://picard-docs.musicbrainz.org/en/config/options_plugins.html

[Aerozol]

Nice one @phw. How much padding should be in the icon itself was something I wasn’t sure about.
I uploaded bigger ‘trash’ icons into the ticket for you to use :)

[phw]

@Aerozol @zas Updated to use the new icons. I also added some extra spacing between the buttons, which makes this UI look cleaner.

And here a screenshot using the trash bin icon:

I personally prefer the cross and would go with that (it's also what is currently in the PR). What do you think?

[zas]

I personally prefer the cross and would go with that (it's also what is currently in the PR). What do you think?

No strong preference, but I'm fine with cross

[zas]

LGTM

[Aerozol]

Looks great! Visually I much prefer the cross, hopefully it doesn’t cause any confusion.