Add an ability to collapse tab-space [feature-request]

[ngo]

Currently we are able to collapse the contacts part of the main window, which is good. But no ability to collapse the tab part. This results in an ugly blank space when no tabs are opened.

[mandyzhou]

I'm not sure that collapsing the tab area would be the best idea. Either the whole window would have to be resized, or the contacts list would be stretched way too much. I think a nice alternative way of dealing with the ugly blank space would be to put a logo or text overlay in the middle of the area, e.g. "Select a contact to begin talking."