Feature request: adjustable Fourier mask attribute

[bmorris3]

In the weekly telecon, @LaurentRDC requested, and @jkentwallace seconded the request, to:

1. Make a more general interface to the Fourier mask, such that the mask is an attribute that can be edited, and reconstructions repeated with the updated mask.

2. Save the raw Fourier mask within the HDF5 archive, so that reconstructions are reproducible.