[Highlighters]: change buttons to "flagged" buttons in sets lists

[PetbkA]

After #534 I've started to enable only the approriate highlighter sets, depending on the log I'm viewing.

The problem is that sometimes I need to enable e.g. 3 sets and disable couple of others at the same time. Now I have to open menu → Click on one of sets (Menu will be closed) → Open menu again → Click on the other set (Menu will be closed) and so on.

It's better to do this on one menu opening, so I proprose to change highlighter sets buttons to "flagged" buttons, so clicking on sets wouldn't close the menu but only changed set's state.

Also flags for sets would be nice in Configure highlighters... menu - for example to see the effect of set you've just created. Of course, setting flag on Space button and selecting several sets (including selecting all on Ctrl + A) would be nice.

If #502 is planned to be implemented someday, it should be kept in mind while implementing this one

[nowhszh]

I also use this feature a lot, and it does have a bad interaction experience when selecting multiple highlighters, so I implemented this issue. before merging you can download it via the CI product https://github.com/variar/klogg/actions/runs/5753292015?pr=660#artifacts

[PetbkA]

23.08.0.1580 x64 Qt6 - implemented and works OK in HL sets list, which, I guess, is fine for 99% users. Still no flags for HL sets in menu (although I doubt that it's easy to implement and thus needed at all).

Also it would be nice if None would also work like flag, i.e. "unchecking" it back would enable all HL sets that were enabled before None was "checked"

[nowhszh]

The function of “None” is to deselect the selected HL, when no HL is selected it is unavailable, the available and unavailable states are displayed differently to indicate availability. I think what you want is a separate function to select all HLs and deselect them all, more like an upgrade to “None”.