Update outputs of EPA app

[jcoulter12]

This is a small PR updating various outputs and print statements.

Summary of changes:

• tau.py plot script is updated to match some relatively recent change by matplotlib which was causing it to crash.
• 1 and 2D unit conversions for Wigner transport output were previously flipped
• Chemical potential determination could previously crash if far too many MPI procs were used
• EPA app now properly prints progress during Fourier bands calculation
• EPA app now outputs DoS to json
• General increase in verbosity in print statements of EPA app
• Added "thickness" input variable for use with 2D systems
• Variational solver now runs for at least several iterations by default to avoid spurious convergence claims
• Added a function to print the dynmat to HDF5 if needed