ubuntu18.04: Update python to 3.7

ubuntu18.04/base/Dockerfile

@@ -52,16 +52,16 @@ RUN apt-get update && \
         libwebsocketpp-dev \
         libfreetype6-dev \
         libharfbuzz-dev \
-        python3 \
-        python3-dev \
+        python3.7 \
+        python3.7-dev \
+        python3.7-venv \
         python3-pip \
         python3-setuptools \
-        python3-distutils \
-        python3-venv && \
+        python3-distutils && \
     curl -sSL -o /usr/local/bin/linuxdeployqt https://github.com/probonopd/linuxdeployqt/releases/download/5/linuxdeployqt-5-x86_64.AppImage && \
     chmod +x /usr/local/bin/linuxdeployqt
 
-RUN python3.6 -m pip --no-cache-dir install \
+RUN python3.7 -m pip --no-cache-dir install \
         graphviz \
         opencv-python==3.4.5.20 \
         nose \

ubuntu18.04/cuda-devel/Dockerfile

@@ -26,6 +26,6 @@ RUN apt-get update && \
         -G Ninja && \
     ninja -C build && \
     cd python && \
-    python3 setup.py install && \
+    python3.7 setup.py install && \
     apt-get clean
 ADD mxnet_profile.sh /etc/profile.d/mxnet.sh

ubuntu18.04/devel/Dockerfile

@@ -25,6 +25,6 @@ RUN apt-get update && \
         -G Ninja && \
     ninja -C build && \
     cd python && \
-    python3 setup.py install && \
+    python3.7 setup.py install && \
     apt-get clean
 ADD mxnet_profile.sh /etc/profile.d/mxnet.sh

ubuntu18.04/jupyter/Dockerfile

 FROM git.imp.fu-berlin.de:5000/bioroboticslab/robofish/docker:cuda-devel-ubuntu18.04
 
-RUN python3.6 -m pip --no-cache-dir install \
+RUN python3.7 -m pip --no-cache-dir install \
         numpy \
         scipy \
         matplotlib \