Allow showing windows (not apps), displaying multiple rows, config from cmdtab.ini

[prechelt]

I have always used a lot the old-style Windows Alt-TAB behavior: All windows listed (not only apps) and shown as icons (not those dysfunctional window previews). Then I switched to a recent version of Windows 11 where this behavior is no longer available even with prodding the registry.

I found https://github.com/hdlx/AltAppSwitcher, which basically does what I need, but is too slow (laggy to appear) for constant use and shows too little information for finding the right window quickly.

Then I found cmdtab, which was much faster. It did not do what I need but appeared to have an understandable code base, so I tried to help myself. It worked. This PR is an alternative solution for #19 (competing with, if I understand correctly, PR #20). Hi @enoversum!

This PR has a fairly tidy sequence of commits; see README.md section "1.6.0" for a summary.

If you accept this, the next steps in this direction would be turning some of the current constants (colors, font size, etc.) into further settings.