feat(theme): Force color to black by default, add theming option

[tecc]

better-theming: The CSS selector now also applies color: black to go with background-color: white.
option-force-light-theme: A new option has been added that forces the colours to always be white for the foreground and black for the background, otherwise inheriting the colours. It is on by default to be as close to original behaviour as possible.

[tessus]

Thanks for your contribution. With PRs like these "before" and "after" screenshots help a lot to decide whether it should be merged. This is just my personal opinion, since this is Laurent's plugin, I won't be able to make and decisions anyway.

[tecc]

Current behaviour:

New behaviour, forceLightTheme = false:

New behaviour, forceLightTheme = true:

[tessus]

I like this change, although the default should probably be the previous behavior, otherwise you break people's current setup. I use the dark theme as well, but in certain situations I like the light theming look better. Having played an instrument in the past, music sheets with anything other than a light background are rather alien to me.
Let's see what Laurent thinks.

[tecc]

The "Force light theme" option, which forces the black foreground/white background combination, is by default on.

[tessus]

Yes, but it wasn't before this PR, was it? So people who install the new version (after this PR is merged) will see the forced white background. This "breaks" their setup.
When you add a feature it should not change the default behavior (except in rare circumstances)

I misunderstood your sentence. All is good.