Improving nested autoeditor menuing.

Example:

    Abjad IDE - materials - talea rhythm maker (Bača)

       1: __init__.py
       2: __metadata__.py
       3: definition.py
       4: illustration.ly
       5: illustration.pdf
       6: output.py
       7: versions/

          definition.py - autoedit (da)
          definition.py - check (dc)
          definition.py - open (do)
          definition.py - output (dp)

          illustration.ly - interpret (ili)
          illustration.ly - open (ilo)
          illustration.pdf - open (ipo)

          output.py - check (oc)
          output.py - illustrate (oi)
          output.py - open (oo)

    > da

    Abjad IDE - materials - talea rhythm maker (Bača) (EDIT)

       1: talea (t): Talea(counts=(1, 2, 3, 4), denominator=16)
       2: split divisions by counts (sdc):
       3: extra counts per division (xcd):
       4: beam specifier (bs):
       5: burnish specifier (rs):
       6: duration spelling specifier (dss):
       7: tie specifier (ts):

          done (done)
          set to none (none)

    |> 1

    Abjad IDE - materials - talea rhythm maker (Bača)

       1: talea (t): Talea(counts=(1, 2, 3, 4), denominator=16)
       2: split divisions by counts (sdc):
       3: extra counts per division (xcd):
       4: beam specifier (bs):
       5: burnish specifier (rs):
       6: duration spelling specifier (dss):
       7: tie specifier (ts):

    Abjad IDE - materials - talea rhythm maker (Bača) - talea (EDIT)

       1: counts (c): (1, 2, 3, 4)
       2: denominator (d): 16

          done (done)
          set to none (none)

    |>