High priority: add filters for the multi-value attributes

[ZoeAffinity]

They have a stack of key:value pairs, where the value is TRUE or FALSE, mostly FALSE, and we just want the TRUE one. The place to fix this is in FilterControl.js around line 150.

[ZoeAffinity]

It's more complicated than that - the field values that are objects full of Booleans need to be cooked down into arrays full of tags (example with this kind of data structure: http://stackoverflow.com/questions/17524627/is-there-a-way-to-tell-crossfilter-to-treat-elements-of-array-as-separate-record ). Meaning, we have to parse and alter the GeoJSON before we concatenate it and feed it to the filters.

[ZoeAffinity]

For now we're just going to parse the "Referral Method" field into a two-value filter (Directly Accessible or Referral Required).

[ZoeAffinity]

I've added a "Referral Required" field. I notice that there are only three services in the dataset so far that accept "No referral".