Generalized spectral analysis (finite volume and DG data)

[JunoRavin]

Complete Samantha's work integrating new spectral analysis features into the postgkyl pipeline, and extend to magnetized simulations where one would like the 1D parallel/perp spectra (relative to the magnetic field).

• Command line/script versions of isotropic spectra computation
  ** Include in documentation a neutral turbulence Taylor-Green vortex problem, whose 1D isotropic spectra can be visualized at the command line (and in a script) at a single instance in time, and averaged over a large amount of time (multiple nonlinear turnover times). At least in the script (preferably at the command line as well) include the k^{-5/3} reference spectra

• Command line/script versions of parallel/perpendicular 1D spectra
  ** Include in documentation a 2D Orszag-Tang (5 moment) turbulence calculation, and visualize the 1D parallel and 1D perpendicular spectra of the magnetic field energy using a command line chain and a script, at a single instance in time, and averaged over a large amount of time (multiple nonlinear turnover times). At least in the script (preferably at the command line as well) include reference spectra

• Spectral analysis should be usable with interpolated DG data (documentation could include link to download magnetic field data from 2X3V Vlasov simulation of Orszag-Tang turbulence, with input file used to generate the data and a note on computational cost)