Blacs Themes

[Json-To-String]

This is a first attempt at implementing labscript-suite/labscript-suite#98 and introduces minimal changes to add some out-of-the-box themes to Blacs. I have some ideas of how to better integrate this approach into labscript as a whole (e.g. moving the themes into a common package so that all components can share them) but I wanted to put the PR up to get some eyes on it and so people could test the feature.

To select a new theme, this PR adds a button in the "File"->"Preferences"->"GUI Theme" field, where you can select from the supported themes or even add your own:

I've currently run this on a few different computers, and it is pretty trivial to add new themes, which live in labscript-suite/blacs/blacs/plugins/theme/themes/*.qss. You can make your own by copying any one of these files and changing the hex values, which VS Code has a nice menu for:

In the works is a way to specify a wavelength that goggles will block, and for the theme to intelligently populate colors that are easier to see.

[Json-To-String]

With the recent update to support Pyside6 and PyQt6, it'd be better to edit the palette instead having a specific stylesheet, so either I'll close this in favor of that solution or edit this PR to include that logic. This ideally should be extended to all labscript components, and we expect that the only component that should take more than providing a palette would be runmanager, since the colors are defined differently for highlighting globals/groups.