Sidebar issues

[PeterC-DLS]

There's some problems with the sidebar from inspecting the source of each page:

• sourcelink.html#L13 points to the wrong repo
• the contributor avatars code does not work
• having this copies in the whole source tree as _source which is unused
• the NeXus info nexus.html is malformed - it should be partial document that is included and use tags properly

[PeterC-DLS]

Fixed by #24 and #25