Null shader and Frame Analysis capability

Aded "vogl_analysis.py" script that can be used for frame performance analysis using NULL FS substitution.

Added NULL_FS capability to FS PP.  Currently this option is given on the vogl cmd line via the "--fs_preprocessor_options <opts>" arg and then consumed by FS PP before passing any remaining options to FS PP.  Basic syntax is "NULL_FS[ID#]:r,g,b,a" where optional [ID#] will only NULL a single FS, and optional r,g,b,a floats will use color other than default purple.