[dwm] buttonpress pull request

This is the buttonpress pull request I have just talked about (incremental to
the domax pull request). It adds a lot of new functionality, i.e.:
- It reverts the "old" zooming with middle mouse button (or toggling
floating if not in tiled layout) with a click inside the window
(+ModKey) or in the bar.
- With the mouse wheel in the bar you focus prev/next client.
- Moving and resizing clients with buttons 1 and 3 also works with a
simplistic click (without modifier key) inside the bar, at the right of
the layout symbol.
- When moving windows, the pointer is wrapped to the top-left corner
of the client, this is also a convenience to go to a window from the
bar after focusing it with the wheel.
And all this in few lines and without damaging too much the code. I
know dwm is by definition keyboard driven, but if there is any
interest I will update the pull request after the 5.0 release (adding the
corresponding pull request for the man page). I find it pretty handy.
I also have pull requestes to view previous tags when trying to view the
current tags (instead of losing the revert state) and to move windows
on screen when you focus a partly offscreen client (this one is like
having an ultra wide monitor :). With these changes I have everything
I want, but I won't send pull requestes for 5.0 to the list if there isn't
any interest.

Have fun,

-- 
- yiyus || JGL .