Cosmetic improvement in 18.04

Dockerfile

@@ -190,6 +190,7 @@ RUN dpkg --add-architecture i386 && \
         xfce4-whiskermenu-plugin \
         xfce4-xkb-plugin && \
     apt-get install -y libreoffice && \
+    cp -rf /etc/xdg/xfce4/panel/default.xml /etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml && \
     if [ "${UBUNTU_RELEASE}" = "18.04" ]; then apt-get install --no-install-recommends -y vulkan-utils; else apt-get install --no-install-recommends -y vulkan-tools; fi && \
     # Support libva and VA-API through NVIDIA VDPAU
     curl -fsSL -o /tmp/vdpau-va-driver.deb "https://launchpad.net/~saiarcot895/+archive/ubuntu/chromium-dev/+files/vdpau-va-driver_0.7.4-6ubuntu2~ppa1~18.04.1_amd64.deb" && apt-get install --no-install-recommends -y /tmp/vdpau-va-driver.deb && rm -rf /tmp/* && \