Add docs for recognition, user interface and exports

docs/source/recognition/multicolor.md

docs/source/recognition/others.md

docs/source/recognition/recognition.md

docs/source/recognition/setting-up.md

docs/source/section/MeinTest.md

docs/source/tracking/export.md

docs/source/tracking/tracking.md

docs/source/user_interface.md

docs/source/user_interface/images/petrack_ui_with_video.png

docs/source/user_interface/images/status_bar2.png

docs/source/user_interface/images/user_interface_empty.png

docs/source/user_interface/user_interface.md

docs/source/user_interface/visualization.md