New file lmwg.py (and supporting files) from Brian's backenddeel branch.  You can use it to plot
a "primitive" (i.e., not derived) variable in plot set 2.  That's it.  Comparisons with observations
are not possible.
1. Get all variables by default when building a filetable.
2. In get_datafile_filefmt(), nother string in the "source" attribute of a file will make it an
 NCAR file - "Community".
Add LMWG to the dict built by diagnostics_menu().
1. Many new functions to support LMWG.   The LMWG-specific ones will later be moved to another file.
2. Another tweek to extract_filefamilyname().
3. The reduce() method promptly prints an error message and returns None if there is no filetable.
Build with LMWG.
This is the version I most recently used for testing LMWG.