ENH: superbuild use lower case convention for file names

Superbuild/CMake/External_fltk.cmake

Superbuild/CMake/External_gdal.cmake

Superbuild/CMake/External_ice.cmake

Superbuild/CMake/External_itk.cmake

Superbuild/CMake/External_libkml.cmake

Superbuild/CMake/External_monteverdi.cmake

Superbuild/CMake/External_monteverdi2.cmake

Superbuild/CMake/External_muparser.cmake

Superbuild/CMake/External_muparserx.cmake

Superbuild/CMake/External_opencv.cmake

Superbuild/CMake/External_openjpeg.cmake

Superbuild/CMake/External_openthreads.cmake

Superbuild/CMake/External_otb.cmake

Superbuild/CMake/External_png.cmake

Superbuild/CMake/External_proj.cmake

Superbuild/CMake/External_sqlite.cmake

Superbuild/CMake/External_tiff.cmake

Superbuild/CMake/External_tinyxml.cmake

Superbuild/CMakeLists.txt