Allow templates in [FCST/OBS]_VAR<n>_LEVELS and user env vars

[georgemccabe]

To specify a NetCDF level with the time information like FCST_VAR1_LEVELS = "(20150317_0000,,)" we need to have the levels variable be able to interpret filename template logic, i.e. "({valid?fmt=%Y%m%d_%H%M%S},,)"

This requires METplus to be modified to reread the field info variables for each run time, check if there is a template used in any levels, and substitute values if they are used. This functionality would also be useful for the user env vars section of the config files, as users could get any time information they need and set it in an environment variable to be passed to the MET config file. This would allow users with special or unusual cases to be able to tailor their METplus calls to their needs without requiring code changes by the developers.

Could any other config variables benefit from allowing templates? We should think about this and add them.

[georgemccabe]

Template string substitution is now supported in [FCST/OBS]VAR[NAME/LEVELS] and in an [user_env_vars]. Merged into develop.