Improve "remote desktop in the cloud" support

[anjackson]

The current version allows you to start up a remote desktop session when running on Codespaces. The 'trick' was mostly that we needed sudo to make the desktop-lite install.sh work. Originally, due to needing root, this was done on the Toolbox repo, but it makes more sense to do it here, so that's been removed now.

Next steps include:

• Write up a blog on using it, note remote-resizing setting which is very handy.
• Working out if we can do the same on Binder, and supporting that, e.g. https://github.com/jupyterhub/jupyter-remote-desktop-proxy
• Tweak Fluxbox setup, e.g. the menu, to add Tika, DROID and others to the menu as well as fixing the shell (which does not start in bash because of this line).