Add XML Parser when response format is XML

[cassiascheffer]

The reporting API currently requests a response in JSON, but if we submit bat authentication data, we get an error message in XML. Parse this response into a hash and return it to the user.

Currently, the error is raised here:

bambora-client/lib/bambora/factories/response_adapter_factory.rb

Line 16 in de3b299

else raise Bambora::Client::Error, "Unknown Content Type: #{content_type}. Response Body: #{response.body}"