Enable analysis to concentrate on last XX months of community

[luca]

It would be useful to have an analysis and visualization for the last period of time (year / six months), in addition to the all time network.

It gives an idea on the status quo and who is active now. Also it is useful for older communities as InnovatoriPA were there are a lot of old nodes from the beginning which are not active any more and the shape of the network could be somehow different now with the only active ones. Also it is needed for activity management and in showing how each activity changed by time.

[albertocottica]

This was done by the "filter edge by age" functionality on the dashboard, IF it was meant to be for visualizing purposes only. Did we want that? Or did we want the Python script itself to start working from -1 year?