Add default a default listing handler
Add default a default listing handler

List content based on the spec tree. Depends on
https://github.com/wikimedia/swagger-router/pull/15.

Krenair/restbase,physikerwelt/restbase,gwicke/restbase,Krenair/restbase,milimetric/restbase,wikimedia/restbase,d00rman/restbase,cscott/restbase,milimetric/restbase,wikimedia/restbase,Pchelolo/restbase,inverno/restbase,wikimedia/mediawiki-services-restbase,eevans/restbase,Pchelolo/restbase,d00rman/restbase,wikimedia/mediawiki-services-restbase,wikimedia/hyperswitch,eevans/restbase,inverno/restbase,physikerwelt/restbase,cscott/restbase,gwicke/restbase