Create a simple filtering module for ltu-cmass

[maho3]

The goal of this task would be to set up the machinery for applying generic filter cuts on galaxy clustering data, for the purposes of masking / data alignment.

As a first step, we would apply the filtering cuts after the ngc_selection.py step. The filters should act directly to mask or weight the (ra, dec , z) fields (rdz.npy) that we would expect from observations.

We should start with simple cuts (e.g. removal of voids) and gradually progress to more complicated ones (e.g. NN weighting)

We should make a new folder within cmass to apply the filter cuts. This module should follow the conventions and configurations of other pipeline steps.

Definition of done

• [ ] A new module cmass.filter which includes at least one simple filter cut to assign weights to the outputs of cmass.survey.ngc_selection

[maho3]

Tagging @tlmakinen

[maho3]

Completed in PR #27 by @suicee