Milestone: Collection archival, Deep Store and Retrieval

[NeilWeingarten]

We will develop a detailed plan in the next year. In the meantime, we will export collections with a Fedora plugin (https://github.com/fcrepo4-labs/fcrepo-import-export) and store them in bags.

[qjhart]

@EricNebeker This is deferred for the initial rollout, but let's update the description to describe what our plans are, so we can start planning the next steps for that.