Added calibration file support to the JPK driver.

Added calibration file support to the JPK driver.

I'm not sure about my interpretation of the calibration file format.
I've emailed JPK for clarification, so we'll see what they have to say.

Also:
* Check for 'filetype' attributes when loading playlists.  If it
  exists, try to load using the matching driver before going through
  the whole list of available drivers.  This should speed up checks
  for curves that were identified by some previous playlist activity
  (or by hand if the user is generating playlists from scratch).
* Pass curve info into Driver.read().  This allows playlist attributes
  to affect curve loading.  The particular example that motivated this
  was
    <CHANNEL-NAME>_<BASE-NAME>_to_<TARGET-NAME>_calibration_file
  for the JPK driver, but it is a good idea in general.  Experiment
  temperature should probably be set this way vs. its current global
  config setting.
* Added Driver.logger(), to reduce code duplication.