Handle dip uncertainty

[pmpowers-usgs]

It would be nice to be able to handle dip uncertainty for normal faults in the WUS programmatically. That is, use fault geometry and slip rate (vertical in 2008 NSHMP; on-fault adjusted for dip in 2014) to derive magnitudes on the fly. This may be incompatible with those faults that have a-priori magnitudes, or they just need to be separated out.