Added link-style paging and replaced Restless 

Two big things in this pull request.

1. I added link-based paging to the API, replacing whatever Restless used. There’s now a block like this in every list response:
    
        "pages": {
          "last": "http://civic-tech-movement.codeforamerica.org/api/events?page=9", 
          "next": "http://civic-tech-movement.codeforamerica.org/api/events?page=2"
        }

    It will contain `first`, `prev`, `next`, and `last` links with only those that are applicable. I’m loving being able to copy-paste URLs to navigate instead of constructing them from parts, hope API consumers will too.

2. Flask-Restless is gone. The code feels a bit cleaner and simpler to me, with a lot more going on in the `asdict()` methods to compensate for what we were getting from Restless. The model objects appear consistently throughout the API now.