Modernize TrackFitter

• prefer compiler-generated destructors
• prefer Gaudi::Property over explicit call to declareProperty
• prefer inherited constructors
• prefer direct-member initialization
• do not hardwire the return type of fitNodes()
• prefer range-based for loops
• prefer std::find_if on reverse range instead of explicit forward loop, remembering the 'last' valid item
• do not cache msgLevel, as msgLevel already is cached
• prefer inheriting from extends over explicit virtual inheritance
• prefer lambda over stateless struct which provide call operator