Reduce margins/padding for taskbar groups

[isf63]

For most themes. Tested only with the Fusion Qt style. On Clearlooks:

Before:

After:

[stefonarch]

I never use them so I've no opinion about that. But needs testing with all widget styles IMO.

[isf63]

I tested with 'Windows' style. It looks like QSS overrides all properties of the widget styles, at least it looks identical.

[tsujan]

Sorry, but I didn't understand what was the problem that's supposed to be fixed by this change. Can't see an issue in the attached image either.

[tsujan]

I trust @stefonarch's judgement on this. A review is already requested.

[isf63]

Note: There was no bug here - no functionality was broken, this is just one stylistic choice over another.

I took better screenshots - the most important theme is Clearlooks as it is the default.

Ambiance before:

Ambiance after:

Clearlooks before:

Clearlooks after:

[isf63]

@stefonarch

Qt styles only affect components using LXQt Themes for the un-themed parts, any existing theming overrides the widget style always. I tested Fusion/Windows and many Kvantum styles and there was no problem.