Add plotting and probe options for flux, RHS, residual, etc.

[cwentland0]

Right now, the only non-solution field which can be plotted and probed is the species source term. This should be expanded to several other relevant fields, including the RHS, the residual, the unsteady heat release (per #35), and fluxes (which are not currently stored). This simply means adding conditional statements to grab these fields for plotting and probing.