WIP: Galaxy workflow-run export to ro-crate including provenance

[pauldg]

Draft implementation for exporting a galaxy workflow-run to an ro-crate, including the extraction of provenance from the galaxy workflow-run metadata.

[simleo]

I've pushed some (mostly formatting) changes to fix the flake8 and pytest checks, so now the build is passing.

Some files here are taken from cwltool: provenance_constants.py and provenance_profile.py, the latter with modifications to target a Galaxy run. This would require adding the original copyright notice. Since the plan (according to the latest Workflow Run RO-Crate meeting) is to eventually depend on cwltool after some refactoring, however, I guess this is going to change.

[simleo]

Unresolved conflicts have been pushed to the branch

[pauldg]

Unresolved conflicts have been pushed to the branch

I've reverted the branch.