Add a class that exemplifies Java-style package statements in Scala.

You can use this kind of package declaration to put an entire file's
contents into the package.
Use the packaging syntax for class Navigator instead.
Demonstrate how in Scala packaging can be more flexible than in Java.

In the very same file you can nest packages and classes, and even
have multiple packages in the same file..
Show how we can achieve concise access to classes and packages.
Show how symbols in enclosing packages aren't automatically available.

If we move class Ship to an outer scope, without importing, it's
not visible to inner package scopes.
Use _root_ to access the root hidden package.

In this way we are able to access Booster3 from a completely
different package and file.