Same-day updates are not processed #16

After having run a migration, and then updating ASpace resources on the same day, the updated ASpace resources are not picked up in an additional same-day run. Setting the highwatermark back to the prior day does pick up the changed resources. This is non-intuitive.

It suggests that the greater_than comparator with a precision of day means "anything after the end of day", not "anything after the start of day".

If we change this to "greater than the previous day", we will get the changed records from today, but we will also get them repeated for multiple runs on the same day. I think this is ok, as they will already be present in the map table.