[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 :) )