Reduce dependency on OpenCV

[astro-friedel]

Several of the plugins have a dependency on OpenCV, which is fine. However, due to the way the ILLIXR include files are structured most, if not all plugins and the main executable all depend on OpenCV.

For example:
main.cpp:
includes runtime_impl.hpp
includes stdout_record_logger.hpp
includes illixr/data_format.hpp
includes opencv2/core/mat.hpp
But main.cpp does not need openCV.

The ILLIXR includes should be restructured so that only those components which really need OpenCV are including it.