vtkOpenFOAMReader: Multithreaded Reading of case files

vtkOpenFOAMReader now supports multithreaded reading of case files. This feature is on by default, and it can be disabled using theSetSequentialProcessing(true). It can be useful to be enabled when reading large case files that are stored on a network drive. If the case file is stored on a local drive, it is recommended to keep this feature off. Also ReadAllFilesToDetermineStructure has been added, which enables reading only the proc 0 directory to determine the structure of the case file, and broadcast it to all processors. This is off by default, because there is not such guarantee that the proc 0 directory contains all the necessary information to determine the structure of the case file. Finally, several performance improvements have been made to the reader.