kwintabbox: Mate-style task switching

Having moved to KDE from Mate Desktop, we had become very annoyed that no matter what we did we just couldn't configure the task switcher to allow us to switch between windows in a most-recently-used-first, but also unminimised-before-minimised way.

This patch introduces support for this dual filtered task switching which, on looking at forums and previous issues opened, has been a long-requested feature.

We have tried to do it in a way that: first, doesn't break existing configurations, which is why the new option appears at the end of the configuration menu list and ClientSwitchingMode enum; and second: is consistent with how the rest of the switcher system works, meaning this works with all available built-in display styles and does its best to be as performant as possible.

This makes KDE far more usable for us, so we hope the patch is welcome and will be accepted. Please let us know if there are any changes that need to be made for this to happen.