Completed integration of SFR_preproc.py into SFR_classes.py

Generally works, although somehow when trying to run intersect, seems to be missing <rivers_table>river_elevs.dbf</rivers_table>

While it runs the entire preproc algorithm, need to see if other shortcomings exist
Merge pull request #12 from mnfienen/classy

Completed integration of SFR_preproc.py into SFR_classes.py