Lighten the disabled foreground color in the dark theme

[seventil]

While trying to choose the selection colors for a new ListView, I found it hard to choose the ones that would have enough contrast by themselves but also had contrast with disabled TableViewLabels in the delegate. But this issue existed only for the dark theme.

So I opened the color wheels for the tableview background colors and disabled color:

The contrast between light-theme disabled and background is ~25, but for dark theme it's just ~10.
Considering that dark-themed contrast shouldn't be 1to1 match to light-theme, I tried changing the color for the label to bump the contrast up. Here is how it looks with 666 color (17 points difference from the background): the type label has the original disabled color, while atoms column has the new 666 color.

[AndrewSazonov]

Looking back at the EasyDiffraction work, I now remember that I changed themeForegroundDisabled to themeForegroundMinor in several places for a similar reason. It was not about selection, but about making non-editable text easier to see against the background. So I am fine with merging this for now, because the new color makes disabled items clearer in dark mode. Later, we should discuss whether we still need both themeForegroundMinor and themeForegroundDisabled, or if they should be merged into one.