Add DB metadata to research updates

[danitrod]

Currently Research updates are being stored in an array in the Research object. The updates should be populated with DB metadata such as _id, _modified and _created, but currently aren't because they're not a standalone db entry. This could be solved either:

• injecting the metadata into an update every time it is created/updated
• moving updates to a separate collection and reference them by id in the Research object.

I'm thinking the latter option is probably the way to go, as we don't want to be managing the metadata manually.

Context: #1110 (comment)

[danitrod]

Using the first approach for now (#1116).