[web] Added coupling icons by @OlafKolditz.

web/static/images/coupling-icons/basic-tet.svg

web/static/images/coupling-icons/basic-tet_BACKUP_73033.png

web/static/images/coupling-icons/basic-tet_BASE_73033.png

web/static/images/coupling-icons/basic-tet_LOCAL_73033.png

web/static/images/coupling-icons/basic-tet_REMOTE_73033.png

web/static/images/coupling-icons/c-tet.svg

web/static/images/coupling-icons/cnh-tet.svg

web/static/images/coupling-icons/h-tet.svg

web/static/images/coupling-icons/h2-tet.svg

web/static/images/coupling-icons/h2m-tet.svg

web/static/images/coupling-icons/h2t-tet.svg

web/static/images/coupling-icons/hc-tet.svg

web/static/images/coupling-icons/hh-tet.svg

web/static/images/coupling-icons/hht-tet.svg

web/static/images/coupling-icons/hm-tet.svg

web/static/images/coupling-icons/m-tet.svg

web/static/images/coupling-icons/t-h-m-c-tet.svg

web/static/images/coupling-icons/t-tet.svg

web/static/images/coupling-icons/th-tet.svg

web/static/images/coupling-icons/th2m-tet.svg