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 suggest to use unsigned in this PR as it is consistent with current `Element::getNNodes()`. 
Later you can send another PR which propose to change type of `Element::getNNodes()` to short and also change the type here.