[0.5]: unify exception handling

[gehrisandro]

This PR unifies the exception handling between the different request types and HTTP client implementations:

• stream requests are now checked for a json response error and throws the corresponding ErrorException like object or content requests already do.
• Guzzle ClientExceptions are checked for json errors before throwing the TransporterException and throw a ErrorException instead.
  Background: For client errors (4xx) the API returns a json error but this wasn't handled with the Guzzle Client yet because Guzzle throws an exception instead of returning the response like the other HTTP clients do.

This change from TransporterException to ErrorException for 4xx responses with the Guzzle Client is a (minor) breaking change!

This resolves #90