Log to the logs/ directory when running with the cucumber configuration

Fixes #5
Implement checking JSON response bodies in the cukes
Update the health feature to properly parse/compare JSON with the new step
Include sourceUrl and version in the Artifact model

This also includes a new migration, which isn't technically needed but gives me
the opportunity to exercise the migrations code a bit more

Fixes #4
Default to UTC as the server's timezone immediately after instantiation
Add the @freezetime tag for stopping Joda time inside of cukes
Implement the processTemplate() helper method for rendering mustache templates in cukes

This makes it possible to write API docs/acceptance tests using "{{foobar}}"
placeholder values that are generated at runtime for things like timestamps or
auto-incrementing IDs

Very similar to the approach we use for our Cucumber/Ruby acceptance tests via
the lookout-rack-utils gem: <https://github.com/lookout/lookout-rack-test>