Add postgis to postgres image

[galbwe]

Branch off of docker-compose. Add a directory with a Dockerfile for a postgres database with postgis for storing spatial data. A good image to work off of is here. Update docker-compose.yml to use the image build from the dockerfile instead of the vanilla postgres image.

[galbwe]

Currently working on this on the postgis branch. I've also been doing some data cleaning here, so maybe we either fork this branch or branch of it to keep data cleaning out of the way of dba tasks.