Updated vclamp to use new ColumnAddingCommand.

Updated vclamp to use new ColumnAddingCommand.

Also added 'ignore after last peak info name' argument to
SurfaceContactCommand"

This allows for the two-cycle surface detection mentioned in commit
725a18055518.

  ./bin/hooke -c 'load_playlist test/data/vclamp_wtk/playlist'
              -c 'zero_surface_contact_point --block retract'
              -c 'flat_filter_peaks --block retract --min_points 1'
              -c 'zero_surface_contact_point --block retract
	              --ignore_after_last_peak_info_name "flat filter peaks"'
              -c 'convert_distance_to_force --block retract'
              -c 'remove_cantilever_from_extension --block retract'
              -c 'flat_peaks_to_polymer_peaks --block retract'
              -c 'polymer_fit_peaks --block retract' --command-no-exit

Note that `flat filter peaks`, `flat peaks to polymer peaks`, and
`polymer fit peaks` still need to be updated to ColumnAddingCommand
subclasses.  Also, I might be missing a few column renames in the
above command.  I'll include a working (and tested) command once I get
the other plugins up to speed with ColumnAddingCommand.