Update Validation Endpoints

[perigrin]

This closes #59 but removing the ValidationStatesWithResults array and only expecting a single entity to be returned. This required a minor change to the templates and updating the fixtures to return a 404 instead of a 200 + []

As a side effect, I also updated the make file to handle the fact that I was attempting to run tests in TZ=EST and they were expecting TZ=UTC. I've also moved the dependency management to go mod which comes with Go now.

[karenetheridge]

looks good other than the Content-Length.

I had to double-check, but indeed it might be possible to return a validation_state with no results (the json schema in response.yaml doesn't state a restriction, and it is possible in the database to have a validation_state with no associated results, although this probably would be the result of a database accident, as we should always be creating a validation_state with at least one result (otherwise the plan had no validations in it, or every validation skipped its check, which would be weird) -- so it's reasonable to check for results before printing them.

[perigrin]

kosh, I think, will blow up if we don't fill the struct properly (it'll assume it was a parse error on the JSON I believe). Adding more error checking and a better handling of responses is on my list for next week.