Add PWA functionality (splash screen, maskable icons etc.)

[lorenz-h]

Adresses #127 .

[lorenz-h]

So far I have just added some required tags to the webmanifest and added it to index.html. I think it makes sense to have one default manifest for all views (and storing it in the default view just like the apple touch icons).

The next step will be to generate a number of icons for the app and add a service worker. @tuomashamalainen could you add the icons? I added you as a collaborator to my fork.

[lorenz-h]

I generated a maskable icon from the existing apple touch icon. The icons 300x300px resolution should be sufficient.

[tuomashamalainen]

Thanks for your work on this so far, I'll fold it in.

So far I have just added some required tags to the webmanifest and added it to index.html. I think it makes sense to have one default manifest for all views (and storing it in the default view just like the apple touch icons).

For now this works. The use case for "views" is having different interfaces for different form factors (e.g. I have one that's meant to be used with a Beosound 5) or customised layouts for OEM partnerships. "Default" will always be the general-purpose UI for most devices.