Add initial :JavaNew implementation for creating new types

Supports tab-completed element type (eg: class, interface) as well
as packages for the name of the new Type.

Usage:

  Without a package, the Type is created in the current package
    :JavaNew class Foo

  But package can also be specified
    :JavaNew interface com.example.Bar

  Abstract classes are just "absract" for brevity
    :JavaNew abstract Baz

Limitations:

  Does not yet support packages that aren't already created

This is for #230