Use cargo-make (or similar) for builds

[ivnsch]

The shell build scripts are becoming unwieldy. cargo-make allows to organize this better. We would also handle iOS and Android consistently, be able to call Rust code (could ease e.g. uploading the zips to Github for the universal release) and integrate CI / Github actions, among others.

[ivnsch]

See https://github.com/shekohex/flutterust/blob/master/Makefile.toml for a possible guide. It builds Rust for a Flutter app.