up with convention, down with case.  pubsubhubbub now adhears to ruby caseing, rather than its own name weirdness

Revert "Mount application on proper location" - changes cause app to fail when there's no trailing / on the pod_url.

This reverts commit 18827b40.

When using sub-uri, create a symlink in public/ making the assets
available at the sub-uri. Modify environment.rb so that asset paths
refers to this sub-uri path. Closes http://bugs.joindiaspora.com/issues/391
and http://bugs.joindiaspora.com/issues/737 when application mounted
on suburi (i. e., prev patch)

Uses mapping in config.ru to respect sub-uri settings in pod_uri.