Emphasize minimization in MinimizeAll script

Summary:
MinimizeAll should work as follows:

> As long as there's something to minimize, do that.
> Otherwise unminimize only the windows we minimized
> on last invocation.

Quote above is from Comment 11 by Thomas Lübking of BUG: 356161.

But current code does not fulfill these duties. Try next case: run minimizeall on some windows, then click on one of windows, then run minimizeall again. All windows would be unminimized!

I have tried to make small changes to original code of main.js, but i can't because i don't understand it.

Thats why i wrote my own version. Then i changed my version to version of zzag, because his code is more simple. I have tested both versions.

BUG: 356161

Reviewers: colomar, #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: romangg, zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D24044