serve support document from /.well-known/browserid

For convenience, serve the support document from
/.well-known/browserid in addition to /support.  This reduces
the amount of web server configuration required if the app is
mounted at the root of a domain.

Drive-by dedup a couple of things as well.
remove authentication concerns

Authentication is handled by the web server, so remove the
authentication-related actions and associated sources.
read support documents as JSON

Read the support documents as JSON to simplify both the serving of
these documents and the processing of relative URLs.