remote-desktop-jupyterlab: Rebase to official remote-desktop base

[frazs]

This issue should be enacted only after https://github.com/StatCan/kubeflow-containers-desktop/issues/42 is complete

Once that is ready, it's time to rebase to that latest version of remote-desktop-base, to benefit from updates and be in line with refractors. This will include:

• [ ] Changing any references to /tmp/home_nbuser_default to the new location of home_nbuser_default
• [ ] Bringing into the repo and COPYing in (to /resources/tools, e.g. /resources/tools/r-runtime.sh) r-runtime.sh and r-studio-desktop.sh from the r flavour of official remote desktop; qgis.sh and qgis-2020.gpg.key from the geomatics flavour of official remote desktop.
• [ ] Removing code that replaces the VS Code Python extension (the correct one will already be in the latest remote-desktop-base)
• [ ] Updating the splash page to be based off the official one, but keeping the experimental addition of the button for RStudio Server (this involves the svg icon, an entry in nginx.conf to serve the icon, the HTML for the button, and a modification to the CSS so that an uneven amount of buttons will have the last element centered)

[frazs]

Actually once the /tmp/ fix is in, it may be worth trying to rebase to remote-desktop-geomatics, instead of bringing in the scripts/key and installing RStudio Desktop and QGIS in the Dockerfile (RStudio Server would still need to be installed). There were issues doing that initially and still having those 3 components work, but they may be possible to resolve (between the /tmp/ fix to be done, and an already implemented fix to r-runtime.sh that prevents skipping components) or find a workaround for.