GitLab

- style with clean-jsdoc-theme (supports dark mode)
- add tutorials (jaguar has a problem with this structure)
- move doc gen stubs to doc_gen folder

This change moves the generated JS API docs from /luci/jsapi
to /luci via README.md which forms the index, and shall
point to a generated html file which exists. It currently
points to LuCI.html, which depends on JSDoc naming
conventions. So it's possible the link can break if modules
change names. But the TOC is always valid.
Signed-off-by: Paul Donald <newtwen+github@gmail.com>