Change theme to 'Light' because 'Modern' has bugs

[merlijn-sebrechts]

The current default theme (ReactOS Modern) is subtly broken: https://github.com/snapcrafters/sommelier-core/issues/10

This switches the theme to the Light theme by Wine developer Zhiyi Zhang, which is a lot more polished.

• Before:
  

• After: (slider now has background)

fixes: https://github.com/snapcrafters/sommelier-core/issues/10

Note to reviewers

This repository contains the source for a part used by a bunch of different snaps. Examples:

• notepad-plus-plus: https://github.com/mmtrt/notepad-plus-plus
• Photoscape: https://github.com/snapcrafters/photoscape/

You can test it by cloning the repo of one of those snaps and changing the sommelier part to this:

  sommelier:
    plugin: make
    source: https://github.com/galgalesh/sommelier-core.git
    source-branch: wine-light-theme

Rebuild the snap and install it locally. You can see dialog of the first screenshot by running <snap-name>.wine winecfg.

Note: This is the second try for a new theme. The first try had a few regressions.

[merlijn-sebrechts]

@mmtrt the volume slider in foobar2000 is slightly better

[merlijn-sebrechts]

• @mmtrt Can you review this too to make sure everything is rendered correctly with this new theme?
• @diddledan for context; we decided not to go through with the previous theme change because it introduced some additional bugs. This theme should be perfect.

[mmtrt]

@galgalesh looks and works good didn't any ground breaking issues apart from this side cut off.

[merlijn-sebrechts]

Great, thanks @diddledan !