Add configurable application name to CTRConfig

[cohaereo]

Currently, the application name in the metadata of a built 3dsx/smdh file uses the cargo package name of the crate that was built. This severely limits the names that can be used, as package names have strict naming rules:

The name must use only alphanumeric characters or - or _, and cannot be empty.

This PR allows users to configure the name through the cargo-3ds metadata keys instead. It will still fall back to the package name if a name isn't specified