Replaced dependency for kriswallsmith/buzz with guzzle/http

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | sorta
| BC breaks?    | yeah baby yeah
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Not much to say. Everything's in the title.

I actually also replaced HttpKernel's LoggerInterface with Psr\Log's LoggerInterface, in Api and OAuthConsumer