Validate accordingly with content-type defined in spec

[rafaelcaricio]

Fixes #203

Connexion should validate the schema of responses that have content-type as JSON.

Changes proposed in this pull request:

• Validate using json-schema only responses of operations that produces JSON.
• Makes it possible for Connexion applications to return binary data in operations.

[coveralls]

Coverage decreased (-0.2%) to 99.243% when pulling f360295 on rafaelcaricio:verify-content-type into 5e7c946 on zalando:master.

[hjacobs]

🙈 decreasing code coverage..

[coveralls]

Coverage increased (+0.0006%) to 99.458% when pulling a2fc4a8 on rafaelcaricio:verify-content-type into 5e7c946 on zalando:master.

[rafaelcaricio]

Going up again ☝️

[jmcs]

Using parenthesis here would look better than using line continuations ('').

[coveralls]

Coverage increased (+0.003%) to 99.46% when pulling d99152c on rafaelcaricio:verify-content-type into 5e7c946 on zalando:master.

[coveralls]

Coverage increased (+0.003%) to 99.46% when pulling 5c4d12f on rafaelcaricio:verify-content-type into 5e7c946 on zalando:master.

[jmcs]

👍

[hjacobs]

👍