Accept domain as an argument to CreateCollaboration + update specs

[#79958812]

So it's consistent with existing pattern for individual runs.
Update controllers to use new CreateCollaboration + tiny refactoring

[#79958812]

The whole runs creation / lookup definitely requires rethinking,
as it's really difficult to work with this code and would be even
worse after collaboration stuff is added.
Rename collaboration_endpoint_url to collaborators_data_url

[#79958812]

That reflects Portal API better and I hope it's clearer.
Unstick runs which have the wrong Activity / Page combination in sequence runs. [#80388210]

Further work: Figure out how this is happening.  @scytacki thinks this might be happening on the
"Next" button at the end of activities.

https://www.pivotaltracker.com/story/show/80388210