added a minimum layer thickness parameter to the layer mesh generation process
adjusted the dialogue to ask for the new param
Merge pull request #548 from endJunction/DenseMatrixOptimizations

Dense matrix optimizations
[ML] Reformating.
[ML] Data structure for storing properties.
[ML] Impl. of addProperties() and getProperties().
[ML] Docu in class mesh: addProperties() / getProperties().
[T] Test for properties in class Mesh.
[ML] Move property implementation to separate file.
[ML] Add MeshItemType parameter to getProperty and addProperty().
[ML] Impl. of PropertyVector.
[ML] Using PropertyVector in class Properties.
[T] Update test.
[T] Try to fix tests on travis.
[ML] Remove unnecessary includes.
[T] Specify the MeshItemType in the test.
[ML] MeshItemType is not longer a default argument.
[ML] md Shorter notation.
[ML] Cleanup unused constructor.
[ML] Remove the mesh from Properties.