Implemented new mapped function.

Summary: SegmentPackageWrangler now implements (dme) command.

Description: 'all - definition modules - edit' (dme) lets the composer edit the
definition.py modules found in all segment packages.

Example:

   Red Example Score (2013) - segments

      1: segment 01
      2: segment 02
      3: segment 03

         segments - copy (cp)
         segments - new (new)
         segments - remove (rm)
         segments - rename (ren)

   > dme

   Will edit ...

      /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_01/definition.py
      /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_02/definition.py
      /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_03/definition.py

   Ok? y