Create UI to list and download outputs created by a pipeline

[pombredanne]

Today a pipeline can create new outputs in the /outputs sub directory of the workspace but these are only accessible from the command line.
I would like to have a UI that lists these outputs that I can click and download without using the CLI.

[pombredanne]

We are for now instead creating a dedicated output in the main UI for attribution #684

[pombredanne]

It would be especially useful to get the scancode-toolkit scan from scan_package pipeline as part of #815 so we could fetch the scans completed in the purldb to further determine if there are license detection issues and/or TODO items

[tdruez]

@pombredanne Project outputs are now available as a new REST API project action.

[tdruez]

@pombredanne Outputs panel added in #928