Add single button to clear all filters rather than individual 'x'
buttons.  Fixes #214
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
#19 getFeatureInfo links opening in new tabs except onclick links
Ensure key is a locally scoped var
Specs to ensure that the _clearFilters function exists and is called
Fix for link to WAODN. Removed context from front page links to other AODN portals from all AODN sites.
First pass at DownloadCart handling download requests only