Reorganize and curate applications page

[JeremyMcCormick]

There is too much duplication on the applications page, as some are listed up to three times (IPAC Firefly, for instance).

It might be better to have a curated list, where each application is listed once, along with links to its documentation and "tags" or other indicators as to what services and functionality it provides.

I would also suggest to list fewer applications that are of more general use, as there is a big difference between specialized search tools that would likely be of limited interest versus a well-known, multi-functional application or framework such as TOPCAT or Aladin.