feat(offline): implement service worker

[jeffbcross]

Tasks

• Create broccoli plugin to generate service worker during build
• Cleanup old caches when new manifest
• Implement FALLBACK request matching and configuration (section will be manually edited by developer)
• Implement NETWORK request matching and configuration (section will be manually edited by developer)
• Stretch: delta-based bundle loading and un-bundling

[jeffbcross]

Latest verbal update is that @alxhub is working on a gulp task for this.

[jeffbcross]

And broccoli task since to work with new Angular-CLI-based setup.