WIP: Update of Event/PrimaryVertex in anticipation of use in upgrade reconstruction

Brief description:

• changes to interface to allow using both v1::RecVertex and v2::RecVertex as input
• moved from xml to plain headers to deal with the templates (probaby wouldn't have been necessary in the end, but I'm not quite done.) To be done: use this in primary vertex finders (which are in Rec). Some additional modifications are probably needed for that.