MeshLib add properties

This PR is based on the discussion in PR #531:
- It adds an implemention to manage properties within the Mesh.
- The properties are associated to specific mesh items like mesh nodes or mesh
  elements via an enum class (see enum class MeshItemType).
- The properties are not restricted to a particular data type, you can use several types like double, vector or matrix
  types at run time together (see tests).
- There is not a possibility to get the value data type.
The objects within a ```PropertyVector``` should be destroyed by the destructor of the class ```PropertyVector```. The PropertyVectors itself are stored within a ```boost::any``` which is stored in the ```std::map<PropertyKeyType, boost::any> _properties```. The PropertyVectors are destroyed by the ```std::map``` destructor.