Improvements to reuse of predicates.

* [DATAHUB_DEBUG,DATAHUB_GENERICS,FIX] Improvements to the way in which initialization takes place.
* [DATAHUB_DOWNLOAD,DATAHUB_GENERICS,SC] Moved message collection predicate to generics module.
* [DATAHUB_DOWNLOAD,DATAHUB_GENERICS,SC] Moved URL-2-file converters to generics module.
Added first version of Datahub archive extraction.