* Use reference_wrapper for preprocess bindings * Update tests * add bindings to I420_SINGLE_PLANE and I420_THREE_PLANES * remove init from all classes except PrePostProcessor and add RGBX and BGRX to ColorFormat enum * update test name * add test for taking input and output by name * move ref_wrapper to common.hpp * add common.hpp include to PrePostProcessor * update comment on ref_wrapper