Support map of outputs

[axlbonnet]

Currently gasw handles outputs and when a gasw job is over, it returns a list of uploaded results.
But actually, with boutiques or any other workflow descriptor, each output has an id, and gasw should also provide for each uploaded result what output it is linked to.
So the change is for a GaswOutput to have a Map of uploaded results instead of the current list (and to make the necessary change in the script to support that).