Fixed missing git exe in ExternalProject_Add.
[ML] Reformating.
[ML] Data structure for storing properties.
[ML] Methods for adding and reading mesh properties.
[T] Test for properties in class Mesh.
[ML] Docu. for property data structure in class Mesh.
[ML] Docu in class mesh: addProperties() / getProperties().
[ML] MeshLib::getProperty(): catch exception.

In case a property with the appropriate name is found but the type mismatches there will be thrown an exception. This case a boost::optional with invalid content is returned.
md [ML] Data structures for storing properties.
md [ML] Methods for adding and reading mesh properties.
[ML] Move property implementation to separate file.
[ML] Add MeshItemType parameter to getProperty and addProperty().
[T] Test also Properties::removeProperty().
[ML] Impl. of PropertyVector.
[ML] Using PropertyVector in class Properties.
[T] Update test.
[T] WIP Update test.
[ML] md
[ML] md
[T] md to tests