Collapse edges by double-click if node is already expanded

[Issif]

Hi,

It's useful to be able to expand edges of a node by a double click, it might be useful too to collapse them if we double click on an expanded node.

[paulftw]

Hi, great feature request, but seems to be a duplicate of #50. Closing this one.
Please feel free to re-open if you think you need a different behavior from what's described there.