11 harmonize the nexus web pages convert the current wiki to use sphinx same as the main nexus documentation

[RussBerg]

The old Vagrant based wiki files have been removed and replaced with a sphinx-build just like the standard nexus manual.
Closes #11

Using linkchecker I managed to resolve the internal links such that linkchecker does not report any issues but when I look at external links then there are a great many that have issues such as links to projects that used to exist when the markdown was edited, for example: Project on Github <https://github.com/nexusformat/NIAC/projects/3>__ etc.

Being that the current wiki contains these broken links it is perhaps not an issue?, it would take significant effort to go through everything to remove/fix all of the link problems.

This will need some discussion at an upcoming NIAC technical meeting but before then this PR needs to be reviewed as it likely needs a few iterations.

[PeterC-DLS]

Some points:

• build directory included
• maybe leave the markdown and use a sphinx extension: https://www.sphinx-doc.org/en/master/usage/markdown.html - this will be a lot less churn
• consider deploying a specific website github pages-only repo then we can also add the historical versions of the manual in the same place (need to check what domains are used and whether we need to redirect old domains to sub-directories)