Calculation and service validation improvements

• Currently older GMMs that only support vs30=[760, 2000] throw server side errors when a different vs30 is selected. Need to determine if graceful failure is handled on the client or server.
• Dynamic UHT calculations return results outside the bounds where static curves are calculated and can therefore give a very incomplete hazard results for sites (e.g. northwest Bahamas) towards the edges of our rectangular/mercator map regions.
• Handle out of range deagg return periods and IMLs

Error handling is now done in JavaScript to handle any web service returns with "status" == "error". With this update an overlay is display with the error message and the plot is cleared. However, there could be further handling on the server side, e.g reporting which GMMs can support what vs30. If the client side error handling is satisfactory this issue can be closed.

changed title from Improve range checking and error handling/reporting to Calculation and service validation improvements

mentioned in issue #420 (closed)

mentioned in issue #169 (closed)

changed the description

added GMM label