Support setting min/max values for series analysis plots

[bikegeek]

The current scales generated for the series analysis plots are based on min/max values for a given statistic. This can lead to misleading representations. The user should have an option to define the scales for their data in the constants_pdef.py parameter/config file.

[bikegeek]

Now that constants_pdef.py is no longer employed, allow users to do this in the appropriate MET+ config file, use case config file, example config file, or custom config file.

[bikegeek]

constants_pdef.py is no longer used. Instead, allow user to set min/max values in the appropriate METplus config file (e.g. in a use case, this would be the config file in the parm/use_cases/examples directory)