Update app to work with v2.0.0 of ohana-api

This app now points to the new demo API, which only contains a small sample data set: http://ohana-api-demo.herokuapp.com

In order to let ohana-web-search test pagination, the demo API displays one result per page.

The other notable change is replacing poltergeist with capybara-webkit, which is so much nicer. Not a single error.
I wish I had thought of switching before spending hours fighting with poltergeist. Haven't tried it on travis yet, but we'll see as soon as I push this commit.

I also got rid of the Kind search filter since that's specific to SMC, but we still need to clean up the other places where Kind is used. I also defaulted the service_areas param to an empty string instead of SMC, for obvious reasons.
Update example yml to point to demo API

Also allow app to use different API for tests.
Merge pull request #373 from codeforamerica/postgres

Update app to work with v2.0.0 of ohana-api