WIP: VisIt reader plugin

It will allow to create a visit bridge plugin for custom reader.

Example of CMakeLists.txt:

set(sources
  myVisItReader.cpp
 )

set(_VisItReader_output_dir
  "${CMAKE_CURRENT_BINARY_DIR}")

# used by add_visit_reader to generate vtk reader file.
set(_visit_reader_module vtkVisItReaders)
set(_visit_reader_module_export VTKVISITREADERS)


add_visit_reader(MyReader "1.0"
  VISIT_READER_NAME "avtMyFileFormat"
  VISIT_READER_TYPE "STMD"
  SERVER_SOURCES ${sources}
  )

get_property(visit_server_sources GLOBAL PROPERTY _visit_server_sources)
get_property(visit_db_sources GLOBAL PROPERTY _visit_db_sources)
get_property(visit_db_headers GLOBAL PROPERTY _visit_db_headers)
get_property(visit_include_dirs GLOBAL PROPERTY _visit_db_include_dirs)

vtk_module_add_module(vtkVisItReaders
  SOURCES ${visit_server_sources} ${visit_db_sources}
  HEADERS ${visit_db_headers}
  PRIVATE_HEADERS ${private_headers})