[feature] Regions gain and fades

[wargreen]

Another thanks for another feature request ;)

Also for a better integration in a workflow, it would be very useful to have the PT regions gain and fades (even if fades curves are not exactly the same) in the imported Ardour's session. I can send an example session.

I have to make a mix of a track recorded and edited on PT... So manually redo all theses part of edit is very hard. I think that can be useful for everyone !

Thank you a lot for the work.