gallery examples use low-order integration n Multipole

[Roland Haas]

The gallery examples https://www.einsteintoolkit.org/gallery/bbh/index.html and https://www.einsteintoolkit.org/gallery/bns/index.html extract waveform multipole moments using the Multipole thorn. However the use Multipole’s integration on spheres to compute the modes defaults to just the “midpoint” rule which is only 1st order accurate. Instead we should use the “simpson” rule which is 4th order and quite robust.