Wrote MaterialPackgeWrangler.edit_metadata_modules() tests.

Example: use (mdme) to open the __metadata__.py module in each material
package:

    Red Example Score (2013) - materials

       1: instrumentation
       2: magic numbers
       3: pitch range inventory
       4: tempo inventory

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

    > mdme

    Will edit ...

       /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/instrumentation/__metadata__.py
       /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/magic_numbers/__metadata__.py
       /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/pitch_range_inventory/__metadata__.py
       /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/tempo_inventory/__metadata__.py

    Ok? y

    >