Streamline the API

The API originally followed the pattern of Urban Airship’s public API
v3, which included a wrapper object in each response, which provides
room for status and extra metadata.  However, it makes the inputs &
outputs asymmetric. This change strips that out, just using the raw
entity representations.

The main benefit? We can now easily import/export via the API with
curl, or similar simple HTTP tools. Dashboards can be copied from one
instance of Tessera to another simply by piping one curl command to
another.
Merge pull request #281 from urbanairship/api-streamlining

Streamline the API