LL-410
* extend search call with parameter extendToParents to extend search for parents of found entities as well, e.g. qa threads for found answers
* new SSEntityHandlerImplI method getParentEntities to retrieve parents of given entities (currently implemented in coll and disc service)
* impl. SSEntityHandlerImplI getSubEntities in disc service for types disc, qa and chat
* impl. SSEntityHandlerImplI getParentEntities in disc service for types disc, qa and chat