Cancel Fetch on Unmount (and Other Updates)

[RobertFischer]

This PR does the following things:

1. Add in PropTypes so that we give our users feedback on whether or not they are passing the correct parameters. (They can remove them in production using babel-plugin-transform-react-remove-prop-types.)
2. Capture the promise that is performing the fetch, so that we can cancel it on unmount. This saves a memory leak and a warning message whenever someone navigates away before the fetch resolves.
3. Switch to Bluebird so that we have the promise.cancel() functionality required in Large SVG #3.
4. Chain the promises, so multiple rapid changes would still all be cancelled on unmount.
5. Move off of deprecated React.Component methods to their contemporary alternatives.

[RobertFischer]

If you merge both this and #20, then you'll want to pull from my rcf/ensure-fetch-cancelled-with-debug branch instead.

[seekshiva]

fetch abort has been implemented using AbortController and released in 2.0.10.