Move internal jpackage classes that define jpackage model into "jdk.jpackage.internal.model" package.

This package will contain interfaces, exceptions, and classes defining the properties of bundles jpackage should produce. For now, these are: ConfigException, PackagerException, MsiVersion, and DottedVersion.

This is aligned with the plan to decouple command line parsing and package building suggested in JDK-8333664.

Move PathGroup class to "jdk.jpackage.internal.util" package.