Implemented @sept-en's tip.
VisualizerEditor implements the listener class, with a dummy windowClosed() method.
Derivations of VisualizerEditor can optionally implement windowClosed().

This might be very Cyclops Stimulator specific addition, and there might be a better way to do this:
DataWindow is used only by VisulaizerEditors. So I added a callback to the editor whenever an (open) DataWindow is closed.
I don't know how useful this might be for plugins other than for Cyclops.

Motivation: Since the datawindow is also shared by CyclopsEditors, when a window is closed, only the editor which created the window would get it's windowSelector button toggled back to "off".

With this PR, the button toggles, and the editor's windowClosed callback is called, in which the message is passed to peers through an internally maintained structure -- so that they can toggle their buttons too.

0MQ is included, but not linked (unless you define it in
NetworkEvents.h).
Redrawing events are not called for some reason.

Now follows usual behaviour for this kind of zoom.
Still needs to update the comboBox.

after zooming with shift+scroll.
Also now issues full redraws after range is changed.

Double clicking on a channel display in the LFP Viewer maximizes that channel. Double click again or change spread settings to return to normal mode.

Button::setToggleState (bool, bool) was deprecated in favor of
setToggleState (bool, NotificationType).

Occasionally waits for a whole screen buffer cycle after resuming before
displaying again, possibly a full redraw issue. Generally seems to work
though.

increased draw range