Follow-up from "Adapt to consistent Track Enums" and use strong types in Properties

The following discussion from !2601 (merged) should be addressed:

• @graven started a discussion: (+2 comments)

  Ideally this would now be:

    Gaudi::Property<std::vector<LHCb::Track::Types>> m_tracks{this, "TrackTypes", {LHCb::Track::Types::Long}};

  (not sure if the fact that LHCb::Track::Types can be used as property automatically implies that a vector of them can be a property -- if not, there is a small bit of extra code to make that work, basically add a template specialization -- see eg. here and here)

  As a side-effect, the python code setting this property will have to pass strings which spell out the types instead of just magic numbers that I can never remember anyway...