Mock datasets for MPoL tutorials and tests

`*.npz` and `*.asdf` files containing visibilities are in the TMS format (opposite that of CASA). logo_cube.noise.npz visibilities have been rescaled such that data - model / sigma follows the expected Gaussian envelope. HD 143006 continuum visibilities have flagged outliers removed and weights rescaled such that the data - model / sigma follows the expected Gaussian envelope, for each spectral window. AS 209 continuum visibilities have been averaged across frequency and have their weights rescaled such that the data - model / sigma follows the expected Gaussian envelope, for each spectral window.