Handle custom Vs30

Implement, test and examine interpolation of static hazard curves between site classes.

• NshmNetcdfReader (and associated services) should restrict incoming Vs30 to the range [min..max]
• If exact value present return data, if absent, linearly interpolate the adjacent vs30 curves.
• Only support single location request, not four corners
• Rename and deprecate, but don't eliminate, existing method that requires strict vs30.