Streamline hits used by pattern recognition
Introduces a Hits abstraction in the LHCb::Pr namespace that inherits from Hits in their respective Velo, UT and FT namespaces and templates according to HitType. The original Pr::XX::Hits classes are now hidden in a details namespace. For this to be useful the Pr::UT::HitHandler and Pr::UT::Hits are amalgamated by moving functionality from Rec to LHCb. No other significant hit class changes are put in. To solve dependencies, Track related code is moved from UTDAQ to TrackEvent. Adds test for all three hit classes.
Goes with Rec!2809 (merged), Allen!818 (merged) and Moore!1456 (merged)