Add PWA features to template

[macdonst]

Ran Lighthouse against an app created with this template and it scored:

This issue is to track the improvement of the template adding PWA functionality.

[macdonst]

You can now see a live example of this template at: http://phonegap.com/phonegap-template-vue-f7-blank/#!//

[macdonst]

Because of some url re-writing at phonegap.github.com the live example is now at:

https://macdonst.github.io/pwatest/#!//

[macdonst]

Played around with PWA'ing the template and got it to this stage:

Something went wrong with Lighthouse which is why performance is 0 and we are stuck at 91 on PWA.

[macdonst]

Things I learned:

1. We need to handle icons better. It would be great if we automatically generated icon/splashscreen images.
2. ~~We should add a noscript tag to our main html file.~~ DONE
3. We should add a meta tag with the theme-color attribute and a theme-color in manifest.json. Ideally it should match the color used by F7.
4. The index.html file should have a link to manifest.json.
5. Should include a serviceWorker and the manifest should be automatically generated.

[hollyschinsky]

6. Register the service worker - https://github.com/phonegap/phonegap-template-vue-f7-todos-pwa/blob/master/template_src/www/index.html#L36-L40

[devgeeks]

https://github.com/phonegap/phonegap-template-vue-f7-split-panel/commit/c25c5e11da6f4845163dc0fc7baa9dfd54766166