Creating and destroying work arrays in SEULEX solver

[dholland88]

When using the SEULEX ODE solver in the cfd plugin, there is also a significant amount of work being done by creating and destroying the work vectors every time the equations are being solved. It would be give a decent performance improvement if this could be refactored so that they are only created once and destroyed once at the end of the CFD simulation. This would just require that the same species are being solved for in every cell for every time step, which is generally true.

I have not checked/tested the CVODE solver for a similar issue.