In applyClicked, look at what obs set the user had chosen (previously nothing had ever looked at
what the user wanted, it always had the default value) and set the appropriate file filter.
A substantial but not major refactoring of how the filter menu is treated for observations.
Actually read and use the user-supplied file filter (for model datasets) #1 (i.e. DS1).
It's been around for months but ignored until now.  The way I did it is crude but effective.
We may want to drop this and do it like obs datasets in the future.  Or maybe do something
completely different.
Merge pull request #3 from UV-CDAT/uvcdat-obs1filter

In applyClicked, look at what obs set the user had chosen (previously no...