Over the RenderletManagerImpl renderlets can be registered.
This interface is here for backwards compatibility, the recommended way to
register renderlets is by registering TypeRenderlets as services or by
providing a method provided by the used templating system.
Registeres a renderlet.
For the same rdfType, mediaType and Mode at motst one built-in and one
non-built-in renderlet can be registered. An attempt to register a second
renderlet results in the unregistration of the previously registered one
renderingSpecification - the argument that is passed to the
rdfType - defines the RDF-type to be rendered with specified renderlet
and renderingSpecification and mode.
mode - defines the mode in which the renderlet and rendering
specification has to be used.
mode may be null, that indicates that it is only used when no mode is