add method to load newer sxscatalog files

[md-arif-shaikh]

load_sxs_catalogformat is modified to allow loading sxs waveform files in the new format.

[vijayvarma392]

Also, talk about the Horizons.h5 file in the notebook:

Think of it from the perspective of a new user -- you need to tell them which whiles are good to include.

And make sure the docs printed in the notebook are up to date:

This should already be explaining what new/old means.

[md-arif-shaikh]

Also, talk about the Horizons.h5 file in the notebook:

Think of it from the perspective of a new user -- you need to tell them which whiles are good to include.

And make sure the docs printed in the notebook are up to date: This should already be explaining what new/old means.

I will run and push the updated notebook once the orbit thing is fixed.