Blip integration

@jh-bate A few small tweaks to make it work with Blip.

Impacts on Clamshell:

- You don't pass `superagent` to the constructor any more, just call it with the API url: `var platform = require('tidepool-platform-client')(host)`
- Make sure all dependencies (`_`, `async`, `superagent`) are present on the `window` object in the browser

Let me know if this works out for you?