add video frame decoder, use in fpltool extract

[flipflip8952]

• Add fpsdk::common::cam and fpsdk::common::video to handle FPL CamData (encoded video frames)
• Update Docker images with new dependencies
  • FFmpeg libraries, built manually with --disable-gpl and --disable-nonfree
  • VA-API deps and some useful tools
• Refactor fpltool extract code into class and separate methods for each fpl message
• Add "cam" data extraction to "fpltool extract" and fpltool rosbag"
• CMake stuff
  • Use CMake variables FPSDK_BUILD_TESTING (and ignore BUILD_TESTING) to enable/disable build of tests, default to autodetect and enable if a suitable version of GTest is found
  • Refactor FPSDK_USE_PROJ handling to macro in utils.cmake
  • Add FPSDK_USE_FFMPEG (auto, on, off) for FFmpeg libraries, assert they are free and non-gpl
• Fix installing docu (README.md and LICENSE files)
• Update doxygen/docu for video, fix some Doxygen issues
• Add RTCM3 type 1029 stringification
• Cosmetics