New and improved capabilities for time-of-flight and tracer partitioning computations.

The following fixes and features have been implemented:
 - More robust multidimensional upwind code in class TofReorder.
 - Fix bugs in tracer code of class TofReorder.
 - Add tracer computation capabilities to class TofDiscGalReorder, including limiter for DG1.
 - Properly solve 'loops' (blocks of mutually dependent cells) in both TofReorder and TofDiscGalReorder. This goes for both tof and tracer computations.