Fix redirects on avatarUrl downloading

[caldwell]

The example avatar that the bot uses (http://i.imgur.com/IDOBtEJ.png) is a redirect from imgur now. This wasn't handled and the code tried to upload a zero length avatar which failed. This patch redoes the http fetch using the "request" library (which was already required). This handles the redirects by default and was a little shorter to boot.

I also included another commit which fixes a deprecation message that the matrix-js-sdk was printing:

Returning the raw JSON from uploadContent(). Future versions of the js-sdk will change this default, to return the parsed object. Set opts.rawResponse=false to change this behaviour now.