Add pseudo-dock support to Kwin

Whenever I use instant messengers, I want them to be placed either in the right or in the left, above of all but that other windows are not overlapped by this window.

So I suggest that a new feature should be implemented in kwin: "Dock application". The only thing "dock application" should do is restricting the screen size when changing window sizes (especially maximizing) so that the window is not overlapped by the docked window.

But docked window should NOT automatically
* Make the window top-level
* Remove the window decoration
* Place it anywhere
because this can be done manually

I'll provide a screenshot of what I mean