Class for parallel reading of partitioned mesh data

Along with commit 4cda158,  member function ``stop()`` of class CPUTime and RunTime were removed, and the calling of the function has been removed in the related files.  
i am not sure if we really need to store `act_nodes_ids_of_ghost_element`. The data is secondary information and we can compute them from `elements` and `_nnodes_active`.