Added public travis build for visible sanity check on PRs.

Fixes #20.
Remove S3 from API/edge layers. It is not structured correctly to support multiple respository formats.

This will be further addressed by dictionary/meta-data changes. And
completed with full multiple storage backends in the future.
Merge pull request #83 from ambiata/topic/travis

Added public travis build for visible sanity check on PRs.
Add mima to ivory-api.

Fixes #74.