Substitute enums using enum classes

Pull request is mainly changing the old C-style enums to C++11 enum class. In my opinion the main advantage deploying enum class construct is type safety since the enum values are not converted implicitly to integers.  The enum in C++11 is a type.

I renamed the files MshEnums.{h,cpp} to MeshEnums.{h,cpp} and enum names consisting Msh* to Mesh*.