Web release

[Ciock]

Prepare Rolify to be released on Web.

I see two challenges for this:

• Play audio in the background. Maybe we could be already covered using audio_service without any extra configurations;
• Pick local files with file_picker. This too should be fine without extra configurations, but can we access those local files, which we save the path, without re-importing them every time the user enters the site? If they are imported into the browser cache, we should be able to access them.

[Ciock]

Audio plays fine on Web, but we are left with a big issue regarding file picking from the filesystem.

Using file_picker we can select a file from the computer and access its data (as Uint8list bytes), but not its path. However we can't save these data as local or assets files on Web, so we can't access them later. There is an issue open but with very low prio.

Another way is to host the file somewhere where we can access it by URL, but this means no more full offline app and probably pay for a hosting service. However, I'm open to solutions that go this way.