Additional field required in tblHazard

[wcarthur]

Need to include a field in the tblHazard schema that records the distribution used for calculation of ARI values (e.g. GPD, emp, power). Options are to pull the value from the configuration file, or to read from the global attribute in the netcdf file containing the hazard data. The second option is arguably more reliable, since that is an attribute of the file created by the process that calculates the data. There are situations where a user may create the database in a separate process, using a configuration file that does not have the correct value for the ExtremeValueDistribution option