move error controller to /errors.

By default Apache uses  a global alias for "/error" in the httpd.conf which means that users can not send error reports through MediaCore's error page (because that POSTs to /error/report).

To make things worse Apache (at least up to 2.4) has no "unalias" functionality so a MediaCore operator must always disable the alias for all virtual hosts (often that's impossible to do for example if you're on a shared host).

This change resolves the name clash by using the "/errors" prefix (extra "s" at the end) so error reporting works again also with Apache's default configuration.