Import PWA support from FFA?

[tsilvs]

Unlike desktop version, Firefox for Android supports Progressive Web Applications.

Would be nice to have it in WebLibre to be able to stop relying on Cromite for that and have only a single mobile browser app.

[FaFre]

I started implementing this, but it will require a decent amount of more work to get it done. Basically every app launch spins up a new browser activity which will not work with flutter, so I need to implement another "internal browser" specifically for handling web apps.

To prioritize this accordingly, anyone who also requires this features please like the initial post by @tsilvs