ENH: Add elastix module api

CMake/elxComponent.cmake

CMake/elxModules.cmake

Modules/CMakeLists.txt

Modules/Core/Blueprints/CMakeLists.txt

Modules/Core/Blueprints/include/elxBlueprint.h

Modules/Core/Blueprints/src/CMakeLists.txt

Modules/Core/Blueprints/src/elxBlueprint.cxx

Modules/Core/Blueprints/src/elxComponentDescriptor.cxx

Modules/Core/CMakeLists.txt

Modules/Core/ELXMODULE_CORE.cmake

Modules/Core/ElastixFilter/CMakeLists.txt

Modules/Core/ElastixFilter/include/elxElastixFilter.h

Testing/Unit/CMakeLists.txt

Testing/Unit/elxBluePrintTest.cxx