Add CREDITS to Help section, update License

Rename CONTRIBUTORS.md to CREDITS.md, add names of True Believers,
Blucalculator, contributors from Serval DNA, and Supporting
organisations (linked)

Rename LICENSE.TXT to LICENSE.md, reformat into Markdown

Improve build.xml to translate CURRENT-RELEASE.md, CREDITS.md (renamed)
and LICENSE.TXT (renamed) into HTML in the assets directory, for
inclusion in the Help section