Modularize VTK tree layout

Move source files from their former monolithic VTK location to their new
location in modular VTK without modification.  This preserves enough
information for "git blame -M" and "git log --follow" to connect
modularized VTK files to their original location and history.

Co-Author: Marcus D. Hanwell <marcus.hanwell@kitware.com>
Co-Author: Chris Harris <chris.harris@kitware.com>
Co-Author: Brad King <brad.king@kitware.com>
Co-Author: Nikhil Shetty <nikhil.shetty@kitware.com>