Tidy up and update HTML documentation

[jacklovell]

With the recent additions to cherab.tools, the online documentation could do with restructuring and updating. I would like to get this done as soon as possible so that we don't have to have another labour intensive documentation blitz. This should be completed before the next release of Cherab.

[mattngc]

The new release has now happened. @jacklovell and I met to discuss the required changes to the documentation. We suggest the following inexaustive list:

• The welcome pages should better match github landing page.
• Team section should be totally restructured. Possible categories might be: TMC, local contact points, contributors, sponsoring organisations.
• Publications should be split off into a dedicated page. Ideally showcase a wider range of publications.
• Fix weird line break in the "installation and project structure" section.
• Remove open-adas link from contrib package list.
• Add new documentation section for OpenADAS under Atomic Data -> Section 6.4.
• Remove the warning about EQDSK file format. @jacklovell points out this has put off some users.
• Restructure the tomography section to have two sub headings: 1) Inversion methds 2) Geometry matrices

It was noted that the emission models section needs an overhaul. But this is a much larger body of work and will be tracked separately.