`check-srf` SRF version 2.0 support

[lispandfound]

The check-srf utility has been disabled for a while because it is hard to accurately calculate SRF moment in SRF version 1.0 because it doesn't include the sampled rho and Vs in the SRF file. The new version 2.0 includes this information, and so can be used to calculate srf moment more directly.

Tasks

1. Add a code-path that checks the version of the srf and, if it is "2.0",
2. Calculates the moment using (srf_file.points['Vs'] ** 2 * srf_file.points['den'] * srf_file.points['slip']).sum()