Implemented MakerFileWrangler._list_maker_classes().
Teaching MaterialPackageManager about custom makers.
Taught MaterialPackageManager about custom makers.
Illustrated Blue Example Score sargasso measures.
Improved material menuing.

OLD: filesystem assets appeared before material summary:

    Abjad IDE - materials - example articulation handler (Abjad)

       1: output.py
       2: __illustrate__.py
       3: __init__.py
       4: __metadata__.py
       5: versions/

        * articulation list: ['^', '.']
        * minimum duration: 1/64
        * maximum duration: 1/4
        * minimum written pitch: a,,,
        * maximum written pitch: c''''

          __illustrate__.py - edit (ie)
          __illustrate__.py - edit & interpret (iei)
          __illustrate__.py - interpret (ii)
          __illustrate__.py - stub (is)

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

    >

NEW: material summary appears before filesystem assets:

    Abjad IDE - materials - example articulation handler (Abjad)

        * articulation list: ['^', '.']
        * minimum duration: 1/64
        * maximum duration: 1/4
        * minimum written pitch: a,,,
        * maximum written pitch: c''''

       1: output.py
       2: __illustrate__.py
       3: __init__.py
       4: __metadata__.py
       5: versions/

          __illustrate__.py - edit (ie)
          __illustrate__.py - edit & interpret (iei)
          __illustrate__.py - interpret (ii)
          __illustrate__.py - stub (is)

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

    >