Hard copied aslam_cv2 into maplab to simplify testing and development. It enables better test integration and allows us to remove some code we don't use in maplab but other repos might depend on. Removed doxygen from aslam_cv2 since we are moving away from it being a library and towards a tighter integration.
Switched to using system OpenCV
Updated everything to be compatible with OpenCV 4
Removed the necessity for a custom vision_opencv and increased portability of the code
Removed some hard-to-maintain code for undistorting that was hard copied from a previous OpenCV version
Moved the registration toolbox to maplab_extras to increase maintainability. It has little maplab dependencies so it should remain fairly up-to-date. See the PR for extra info.
Moved maplab_tools to maplab_extras as it wasn't used anywhere in the maplab core functionalities.
Removed the ros-system-monitor package as it hasn't been in use for a long time.
Removing the undistortion code in aslam_cv temporarily disabled the pmvs interface, which should be restored
Tinkered with some unit tests to make them pass:
Stereo package has new values due to the opencv update
Relaxed conditions in the map optimization package to make the test more consistent
Updated end to end test in maplab node
Updated jenkins install and prepare script for Ubuntu 20.04