Update DataFile class to use new time_series_input.xml metadata

A new metadata file named `time_series_input.xml` was added which details the metadata for valid PRMS time-series input variables. Currently the DataFile class does not use this metadata. Further there is a type of metadata created in the DataFile class which relates to metadata that may be found in the data file headers; this may need to be clarified/modified so it doesn't conflict with the metadata for the different input variable classes/categories.