Normalize createdAt/updatedAt timestamps

[ansoncfit]

At least in the modifications collection, some timestamps appear to be saved as NumberLong and others as ISODate

[abyrd]

Can these be normalized with a single update query? I'm guessing it hasn't been done yet just out of caution about blanket-updating a production database.

[ansoncfit]

See https://github.com/conveyal/analysis-ui/pull/878

[trevorgerhardt]

Upon initial creation, objects have proper Dates. But upon first inspection from the UI they have been translated to integer timestamps. This means that upon save/update, those timestamps will be stored as longs instead of as a Date.

At some point conversion is happening on the way to the UI.