Spatial downloads

[chriswhong]

Adds two new endpoints under /projects:

• /download/shp - Downloads a zipped shapefile of all matching projects with their polygons as the geometry.
• /download/geojson - Downloads a geojson FeatureCollection of all matching projects with their polygons as the geometry.

Each takes the same query params as /projects (except for pagination), so the frontend implementation should be to build out a button that hyperlinks to the above endpoints, adding the same query params that are currently in effect in the ZAP Search filter view.

Because shapefile creation depends on ogr2ogr, this PR also adds a Dockerfile. This Dockerfile will be used by dokku to ensure that GDAL (and ogr2ogr) is available in the container this API will run in.

I tested this Dockerfile in a dummy dokku app and it worked, but I didn't test everything manually. We should take care to watch the deployment closely once this gets pushed.

TODO:

• [x] Normalize all download endpoints /projects.{fileextension}
• [x] Cleanup routes/projects/index.html so it's not so crazy.
• [x] Change error code to 500 instead of 404
• [x] Add dropdown to frontend UI for 3 download options

[allthesignals]

Closes https://github.com/NYCPlanning/labs-zap-search/issues/424

[ghost]

don't forget to rebase & squash before merging !!! and maybe for posterity edit the PR description to describe what it actually does now :)

[allthesignals]

This is really hard to setup for local development. Let's get some of these dependencies Dockerized so it's easier to setup fresh!

[allthesignals]

Two things:

• [x] Need to fix running this in CI
• [ ] Squash ur commits into one commit plz!

[allthesignals]

@chriswhong blah, I need help: https://circleci.com/docs/2.0/building-docker-images/