uploadContent: Attempt some consistency between browser and node
Previously, the API for uploadContent differed wildly depending on whether you
were on a browser with XMLHttpRequest or node.js with the HTTP system
library. This lead to great confusion, as well as making it hard to test the
browser behaviour.
The browser version expected a File, which could be sent straight to
XMLHttpRequest, whereas the node.js version expected an object with a `stream`
property. Now, we no longer recommend the `stream` property (though maintain it
for backwards compatibility) and instead expect the first argument to be the
thing to upload. To support the different ways of passing `type` and `name`,
they can now either be properties of the first argument (which will probably
suit browsers), or passed in as explicit `opts` (which will suit the node.js
users).
Even more crazily, the browser version returned the value of the `content_uri`
property of the result, while the node.js returned the raw JSON. Both flew in
the face of the convention of the js-sdk, which is to return the entire parsed
result object. Hence, add `rawResponse` and `onlyContentUri` options, which
grandfather in those behaviours.