Add calc configuration setting to ignore NSHM site-data
Currently, the site-data directory has to be removed or commented out (prepended with '~') in order to not use the site data. This is useful for sensitivity calculations where using site data (basin effects) is not wanted. A configuration parameter to control the use of site-data could default to true to leave the current behavior unchanged.
This setting could be applied when the model is loaded or, more likely, when the list of sites is generated (pass in SiteData.EMPTY instead of model.siteData() to HazardCalc.readSites() if config.hazard.useSiteData == false)