Allow referencing remote assets

[bmicklea]

Describe the problem your feature would solve
When using very large datasets (e.g., image and video data especially), it's painful to have to clone them to my local machine in order to package up a ModelKit.

Describe the solution you'd like
It would be nice if you could provide a URI to the dataset in the Kitfile. I understand that that would trade download time for me for wait time as the ModelKit fetched the data in order to be built...as long as it doesn't happen on my machine 😄

Describe alternatives you've considered
There isn't really an alternative beyond cloning everything locally.

WHEN CLOSED UPDATE THE NEXT STEPS DOC (NEXT-STEPS.MD) WHICH REFERENCES THIS ISSUE.

[bmicklea]

Decision: We'll do this by referencing other ModelKits.