Migrate Flutter part to self-package

[Rodsevich]

From #6 and @DanielArndt contributions I think we should decouple this package from it's Flutter related counterpart in order to have a good script running. Ideally using mono_repo in this very repo, but who knows?

[DanielArndt]

I think that's a good idea, decoupling the packages is probably the right thing to do.