Reduce wave_utils dependencies

[leokoppel]

#231 allows partial build without all the dependencies, but wave_utils is still needed by most modules and requires opencv.

Current behaviour

• wave_utils depends on opencv, just to allow reading into cv::Mat from a yaml file.
• wave_utils contains wave_test.hpp, used by libwave unit tests

Expected behaviour

• wave_utils should not depend on opencv

  • Per CMake: allow partial build and finding components #231, we want to allow building subsets of libwave without needing all dependencies, or just to reduce build time and size.
  • Almost all modules depend on wave_utils, even ones having nothing to do with opencv
  • It seems like bad form to demand a huge dependency for a single use of cv::Mat, not useful on its own
  • We will probably add parser functions for other external classes in future, and should have a way to add them to their own modules anyway

• wave_test.hpp should not be in wave_utils

  • It is not part of public interface - the functions in wave_test should not be installed for users of libwave