add DiscoveryResponse info to SPs in discojson

[enriquepablo]

All Submissions:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what problem you are trying to solve with this PR?
• Have you added information on what your changes do and why you chose this as your solution?
• Have you written new tests for your changes?
• Does your submission pass tests?
• This project follows PEP8 style guide. Have you run your code against the 'flake8' linter?

This adds a discovery_responses key in the JSON produced by discojson for the SP entities that have DiscoveryResponse elements in their metadata.

This is to allow SeamlessAccess to warn users when they are sent to SeamlessAccess with a return URL that does not match the DiscoveryResponse elements published in the SP metadata.

[mikaelfrykholm]

@c00kiemon5ter I am taking a look at this. Setting up env. now.

[mikaelfrykholm]

LGTM. I am working on a test case as well. But this can be merged.