WIP: fix(mobile): re-enable --mobile flag

[jeffbcross]

There are still some todos here, but opening it up in case anyone would like to start taking a look.

CC @gdi2290 @Brocco @filipesilva @hansl @alxhub

TODOs:

• Re-enable mobile e2e tests
• Move module definition out of main-app-shell.ts into app/app-shell.module.ts (make main-app-shell.ts similar to main.ts)
• Clean up temporary directory created during ts compilation step
• Replace the OfflinePlugin with Angular's Service Worker plugin
• Generate manifest.json for Service Worker
• Just pass 'index.html' from webpack-build-mobile.ts to the plugin, let the plugin resolve the path itself.

[hansl]

I'm not going to merge this until the tests are passing and the universal PR has been merged (with this PR rebased on top of it).

[jeffbcross]

Closing this, will give some thought to our CLI integration.

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