Snapshot data source responses for tests

[khaeru]

This would involve:

• Provide distinct tests that make actual network requests. Separate tests of web services/endpoints #90
  • Make these optional for passage of the test suite.
  • Provide some sort of dashboard, integrated with GitHub or the docs, that shows the current status/last failure?
• Take a snapshot of the current responses from all listed sources; add to sdmx-test-data; then use requests-mock (or dsss) to mock those responses for tests.

[khaeru]

#84 expands the set of supported endpoints to all those described by the SDMX-REST standard. This has the effect of increasing the number of source tests to about 572, but also makes it more difficult to follow changes in the endpoints supported by each service. An optional pass/dashboard approach could be even more helpful here.

[khaeru]

Changed the title because #90 achieves the goal described in the original.