[200 hours] Support filter sliders

[rhodges]

Nick wants sliders on arbitrary fields from certain marine life and habitat layers.

For example:
Whale observation points with # of sightings attribute: slider to show all points, or only points with 100 or more sightings, etc...

Solns discussed:

• Major backend work to support this through the layer form for various APIS that could support these queries
  • Lots of work, good result
• Major GIS work to generate all of these layers independently and load them all into the tool
  • Lots of work, difficult to scale once done.
• Sort out the pattern to support these the same way we do with MDAT
  • Some work, no scaling issue, but not promise that data won't change.