Multi-package redux :heart: 

Rather than the current approach of iterating through packages in `vin install [foo|bar|baz]`, we should accept many packages here https://github.com/vinyl-linux/vin/blob/main/server/install.pb.go#L27-L35

At that point we can create a meta-package on the fly when `Pkg` has many packages.

These on-the-fly meta-packages don't need to be added to world.