Store approvedDate date in MapInfo table

[tsa96]

We keep this in the map submission table within the dates field, but normally don't want to include that data for approved maps. It would make a lot of sense to just store an approvedDate date in the MapInfo table alongside creationDate.

I would do this in my current PR, but it's enormous enough as-is, so leaving for afterwards.

[tsa96]

Left a comment in map-info.component.ts in a place that should use this in future.