Introduce separate mock services and data bundles

- Separate mock services into its own bundle, only included if building
  in mock mode (files in mock/ dir)
- Generate data.js from json files included in data/ dir (formerly
  demo/ dir): allows app in mock mode to run offline once loaded
- Update develop.js, gulpfile.js, tests, with new mock services and mock
  data things
- Deprecate "demo" term, use "mock" instead
Add documentation on new mock services and data