WIP: Version track object

• Add inline namespace v1 to Track.xml renamed to Track_v1.xml.
• Add additional namespace Event, so that the full namespace is LHCb::Event::v1::Track(backwards compatible).
• Add Track.h in TrackEvent/TrackEvent/ which includes Track_v1.h.
• Forward declarations in many places need to be changed to include "Event/Track.h".
• Merge request includes adaptions by @roiser to support classes in namespaces in GOD.

Addresses #7 (comment 1755867)