[WIP] Use Guzzle instead of Buzz

The PR is ready, anyway I tag it as wip because:

 - We have bundle to prepare/migrate
 - We need to address few things I'm not really sure (Api::submit method is deprecated in favor of Api::get and Api::post. Does other method are in use ? patch ? head ? So we probably should rename it to createRequest and rovide a BC. I definitely don't like the `submit` word :) )
 - Should we introduce the user agent in this library ? 

 - [x] Use Guzzle
 - [ ] Rename `browser` to `client`
 - [ ] Provide compatibility with PSRLoggerInterface (`err` is not a valid method)
 - [ ] Add backoff plugin + options
 - [ ] Reduce connection timeout
 - [ ] Add UserAgent
 - [ ] Update doc, mention BC break
 - [ ] Move data collector from SensioLabsConnectBundle to this repo as it would be usable in silex provider
I would rather use ``InvalidArgumentException`` here