Support boundary queries

The search framework inserts geometry literals directly into the
query. This presents two problems for the eco service endpoint:

1) There were 10k character being sent in the query string via a GET
request. Solution: Use a POST request.

There are a few oddities worth pointing out here:
  * The ecoservices rest framework expects a json payload to have
  "text/plain" for the content type
  * The previous endpoint would append multiple 'param' parameters like:
     eco.json?....&param=4&param=9...
    Now there is code that specifically looks for and manages the
    "param" key

2) Django serializes the geometry to EWKB

The serialized format isn't great for over the wire json
transfers. Instead we send it as EWKT which requires some acrobatics
Use "mapfeature" as the model for geom searches
Merge pull request #1083 from ahinz/topic/boundary-eco

Topic/boundary eco