Content Negotiation Tweaks

`params[:format]` overrides content-negotiation in rails, so having `format:` in our routes always overrode the value.

To add back browsability (i.e. can click around the API via a browser) we take the requests that rails overrides as HTML only (i.e. direct browser traffic) and serve it as JSON.

Requests made with an accept header of application/hal+json will receive that in their content-type.