Viscosity and conductivity visualization

This PR enables visualization of conductivity and viscosity from IncompressibleNavierStokes and HeatTransfer. To use this, `vis-options/output_vis` should be set to `true` in the input file. Additionally, to get viscosity, `Physics/IncompressibleNavierStokes/output_vars` should be set to `mu` in the input file; similarly, to have conductivity output, `Physics/HeatTransfer/output_vars` should be set to `k` in the input file.

I tested this on an input file from Nick and this worked, but there was something funny happening with the `VelocityAdjoint` function - in dbg mode, it was tripping an assert from fparser. In opt mode, this led to corruption of the viscosity output. I'm hoping that it was just a memory corruption from fparser, but we need to be aware that there is a possible strange interaction happening with viscosity and `VelocityAdjoint`.

I'm merging this into the 0.5.0-release branch, will also immediately merge back into master once this PR is merged.