Update themes to have better support for all the new KColorScheme values.

See #14.

Amongst others, this updates the themes to have nicer positive/negative/neutral colors, complementary colors, and resolves a bunch of colors that look off.

The Blender theme has been updated to fit Blender 4.x dark theme. This may prove a little controversial.

Above: Warning color using negative bg in the qml-fixup branch compared to native warning. This clearly needs a bit more attention to have the forground color get tinted too.

Kirigami Gallery example:

Testing

• Load up this version of Krita
• Check all the default themes.
• Make sure they don't look awful.

Optional:

• Open these themes in Plasma's color config.
• Use plasma for a bit. The themes should hold up just fine.

We're currently not using the focus/hovered/negative/positive/neutral text anywhere, but I hope we'll be able to utilize them.