Improved (mdw*) user experience.

Implemented confirm messaging.

Example:

    Red Example Score (2013) - materials

       1: instrumentation (AE)
       2: magic numbers
       3: pitch range inventory (AE)
       4: tempo inventory (AE)
       5: time signatures

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

    > mdw*
    Will rewrite ...
        /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
        /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/time_signatures/__metadata__.py
    Ok? y
    5 __metadata__.py files rewritten.

    > q