Moves the recently-added vtkWrappingJavaCore module into the
Wrapping/Java directory, and renames it vtkWrappingJava.  This
mimics what was done for Python, and helps to simplify the cmake
process.  There is no longer any need to add Wrapping/Java via
the "add_subdirectory" command, because it is automatically built
when the vtkWrappingJava module is on.

Change-Id: I1a70f78b12b0d79f58769d53a921f721148573f5