paginate the defintions in the mongo store (fixes #254)

[dabutvin]

For documents that have more than 1000 files, we will split them across different documents in the store.

This should be transparent to any callers of the store. we will get and set as one logical document.

Things to note:

• adding a partitionKey set to the canonical coordinates so we can keep multiple pages of a single document on a single partition
• storing currentPage and totalPages as metadata on the document in a _mongo property specific to this store and not surfaced as part of the definition
• working with some larger documents surfaced some bugs in our harvested data around the file lists, we are now treating the clearlydefined tool as the source of truth for absolute file list

[jeffmcaffer]

A few things to check out but otherwise good to go

[jeffmcaffer]

Cool. Ship it when you get those changes in