comparator refactoring

[kjappelbaum]

probably, simply remove all the RMSD stuff. It doesn't work so great.

In general, on wants to be able to preload structures or graphs.

[kjappelbaum]

So, for the redesign we should use

• dask to handle the reduced structures and graphs (either in memory or filesystem or whatever)
• include matminer as dependency to map the structures to a bit higher-dimensional space, search in a region for density but require that p norms and number of atoms are exactly the same. We can get those from pandas.