Modernize TrackMonitors

• fully qualify enums
• prefer ToolHandle over explicit calls to tool<>
• rely on Gaudi calling retrieve on ToolHandle after initialize() is called
• prefer Gaudi::Property over explicit calls to declareProperty
• prefer inheriting constructors
• prefer defaults compiler-generated destructors
• prefer static data in anonymous namespace in .cpp file over static data in local scope (which incurs an atomic check whether the data has (already) been initialized, as that must be done in a thread-safe manner, every time the data is accessed)
• prefer direct member initialization
• prefer range-based for loops
• prefer inheriting from extends instead of explicit virtual inheritance
• prefer free-standing functions in anonymous namespace over member functions
• prefer std::array::fill over std::fill