Making SiDetectorElement thread-safe (ATLASSIM-3931)

Making SiDetectorElement thread-safe by adding std::atomic and std::recursive_mutex for mutable data members.

Mutable data memebers are now guarded by std::recursive_mutex m_mutex (for non-trivial types) or std::atomic (for trivial types) or both.

• Amg::Transform3D
• Amg::Vector3D
• HepGeom::Transform3D
• HepGeom::Vector3D<double>

are not std::is_trivially_copyable and cannot be std::atomic<T>.

https://its.cern.ch/jira/browse/ATLASSIM-3931

RunTier0Tests.py was fine. RunTier0Tests.log