Set accent color based on wallpaper

[meisenzahl]

Supersedes elementary/settings-daemon#25

Requires #1106

Related to elementary/wallpapers#138
Related to elementary/granite#483
Related to elementary/switchboard-plug-pantheon-shell#263
Related to elementary/onboarding#126

[meisenzahl]

Demo in interaction with elementary/switchboard-plug-pantheon-shell#263:

Peek.2021-04-09.23-55.mp4

[meisenzahl]

I had to revert a2da4bb unfortunately, otherwise it doesn't reliably detect when the accent color preference changes.

[meisenzahl]

@JoseExposito thank you for your detailed review and your suggestions! I would be happy if you would find time for a review again 😀️

[JoseExposito]

The code looks good. I didn't go through the colour extractor algorithm with a lot of detail, but it works like a charm.
Once the other PRs are reviewed, we can do test it with everything in place and merge it.

Awesome feature by the way, love it!

[martinstork]

Doesn't this feature need some kind of toggle? As someone who changes wallpapers frequently, but keeps the accent color blue, this wouldn't be a welcome change if it can't be turned off.

[JoseExposito]

@martinstork yes, there is a switch for it here elementary/switchboard-plug-pantheon-shell#263

[martinstork]

@martinstork yes, there is a switch for it here elementary/switchboard-plug-pantheon-shell#263

Oh my bad. Thanks. I tried to move my comment there, but you were too fast 😅