Port webapps to run on flutter

@Lorenzo I think we close this. This was a good idea, but its day has come and gone. 

We have been iterating the work on the flutter homescreen at https://github.com/felipeerias/flutter_homescreen

This is current status of the app view:

https://cloud.igalia.com/s/JMNfNE5EtKfw6ZF

We have an initial ongoing version of the AGL homescreen made in flutter, which for now would be using the entire surface of the screen and emulate the functionalities of some other flutter apps as the application launcher or HVAC by embedding them as views inside it.

https://github.com/felipeerias/flutter_homescreen

https://cloud.igalia.com/s/WNLTxXSec5D8NEM

This first approach of running several applications inside of a single flutter app is something that might be iterated to allow running several apps on different views, being the homescreen just the layout one as we were originally doing. 

I have pushed a repo with the WIP of the flutter HVAC https://github.com/ltilve/agl-flutter-hvac, despite it has pending ongoing work and issues. Also, I will be creating another flutter version of the mixer webapp, so we can also push a newer version of the aglJs connector including the services for it.

After addressing the problems with the assets, we finally have an initial version of the HVAC UI. We are still completing the connections with the services, but can be now run on the desktop (via `flutter` debugger tool on VSCode, or on an emulator), and also bundled for target web as `flutter build web`, and then packaged into an .wgt which can be installed into the image.

For now it's using some standard basic flutter widgets, to target using the same calls as the HTML5 version:

Also, we are testing other more complex Flutter widgets and apps running on WAM, by running the web-bundled version of the flutter gallery app.