Add `steps` and `sleep` options to `move_just_onto_surface()`.

Add `steps` and `sleep` options to `move_just_onto_surface()`.

This takes advantage of yesterday's pypiezo commit:

  commit b66d6dbcb8cd381cf7515a42ab0aee4a4841beb3
  Author: W. Trevor King <wking@drexel.edu>
  Date:   Wed Mar 14 16:18:23 2012 -0400

    Add `steps` and `sleep` options for gentler `jump()`s.

and I've bumped the minimum pypiezo version accordingly.

When I was running some calibrations yesterday, I could hear the piezo
clicking, and after the calibration the deflection was shifted half a
volt or so from the initial deflection.  I attribute this to the
violent piezo jumps shaking the cantilever chip from its original
position.  The wimpy spring-loaded wire clips used in the MultiMode
fluid cells probably aren't helping any either ;).