Added check to prevent display of replica set list page when there are no replica sets.

- Add Unit Tests

The tests cover all methods except the one that interacts with the
client. Test for it will be added later.

This change handles replica set description end-to-end: saving in on the
deploy form and then displaying. It also handles replica set endpoints.
I also attempted to write tests for the go code, but this change grew
too much. I'll do this later.

This change makes it possible to run tests, integration tests and lint
on Travis CI. It also prepares a special Gulp task to perform the same
activities locally. This is handy when, e.g., sending a pull requrest.

This simple setup will be used for handling calls to the API, once
implemented.

It is a little bit overengineered. But I wanted to have go tests for
something. So I made it accept an interface.