Improve operation widget appearance

Operations widget (used in OpenMW-CS for global search, plugins verification and so on) looks like this on Windows:

With two operations it is a bit better, but still weird:

That's because we use a default QWidget height to calculate the widget height, but there is no guarantee that it will fit progress bars height. A suggested solution is to explicitly specify a height reserved for one progress bar.

So summary of changes:

1. Use 40 pixels per line height.
2. Fix margin in QSS - it is misused because a correct order is top, right, bottom, left. Also there was a typo (p instead of px), so there was no bottom margin.
3. Use a different color for a global search progress bar to fit dark themes.
4. Capitalize operation name.
5. Avoid code duplication (default colors are specified twice).

Now it looks like this:

With multiple operations:

With multiple operations and dark style (Fusion):

Note that I do not like an idea to hardcode a separate color for an every operation type - it increases a chance that a progress bar will not look properly with given arbitrary style. Can we just use the same style for all operation types?

Like this.