Changes for #265

The fix: Only include the possible values for Strings and Dates as they're currently the only UI elements that use them.

While I was in there I also added sorting to the Filters so they will always appear in the same order in the Portal. The order is not currently customisable (it's just alphabetical by label).
Updated FilterTests to test changed logic.

Also removed constraints test as we don't do these anymore.
Changes after review #265
Fix remaining whitespace differences
Merge pull request #310 from aodn/Issue265

Changes for #265