[#567] Enable completion endpoint, limit output
[#567] Test that completion keys are limited
Merge branch 'master' into 567-completion-api
Add access check and tests for completion

* _complete endpoint only visible to logged in users.
* Tests to verify access check.
* Re-enable skipped tests.
Merge pull request #568 from openspending/567-completion-api

[#567] Enable completion endpoint, limit output