Docker: added noetic image. Updated travis for focal.

docker/noetic/latest/Dockerfile

@@ -0,0 +1,13 @@
+FROM introlab3it/rtabmap:20.04
+
+ARG CACHE_DATE=2016-01-01
+
+RUN source /ros_entrypoint.sh && \
+    mkdir -p catkin_ws/src && \
+    cd catkin_ws/src && \
+    catkin_init_workspace && \
+    git clone https://github.com/introlab/rtabmap_ros.git && \
+    cd .. && \
+    catkin_make -j1 -DCMAKE_INSTALL_PREFIX=/opt/ros/noetic install && \
+    cd && \
+    rm -rf catkin_ws