Mesh Information View in GUI

Extended the ElementTreeModel to not only display information on a mesh element when it is selected but also on the mesh itself (i.e. if you select a mesh in the MeshTabWidget, detailed information will be shown in the second view).

Currently the following information is displayed for the selected Mesh: 
* Name, 
* number of nodes, 
* number of elements
* number of each type of element that is present in the mesh, 
* bounding box, 
* material ID min and max (if materials between min and max are not present this is not shown!)