Refactor the NNTP table to also store the articlenumber of the server. This way we can prevent searching for the correct messageid if the server is not changed at all. Initial implementation.
When the HTTP NZB provider returns an error, stop it from showing all sorts of warnings on the console of retrieve
Reformat HttpNzb class to be indented properly
Rework the NNTP class to not be a hack of itself any more. We now have proper fields for the different retrieval settings.

Retro modus is no longer a hack, but will allow for a restart from the previous lookup.

If the usenet server is persistent in it's articlenumbering, do not search for the mesageid anymore.