Fixed calculation of dampVal for the case of a pure species condition

In this case, Cantera returns a diffusion coefficient of 0 for the pure
species. dampVal must be positive, so we now take the smallest non-zero
diffusion coefficient.
Evaluate chemical properties in parallel
Replaced SourceTermWrapper with TbbWrapper
Replaced DiffusionTermWrapper with TbbWrapper
Replaced ConvectionSystemWrapper with TbbWrapper
Moved some work into the parallel loops
Fixed a case where ApproxTransport failed to compute the viscosity

The temperature-dependent terms weren't always being recalculated after updating
the set of major species.
Updated performance stats output file

Stats now include time spent regridding and the total run time. Components with
zero time elapsed are automatically excluded.