Fixes required for ROS Melodic support
- OpenCV2 to 3 migration
- Retrain laser detector after OpenCV migration, as old models are incompatible
- Replace deprecated pluginlib macro
- Qt5 support for Rviz plugins
- Replace tf by tf2 message_filter in rviz plugin (contributed by user @f-fl0 in srl-freiburg/spencer_tracking_rviz_plugin)
- Add boost namespace for shared_ptr (for rviz plugin, this was contributed by @makokal in srl-freiburg/spencer_tracking_rviz_plugin)
- Update Dockerfiles