Added 'storehouses - list' (hls) command to wranglers.

Example:

    Score manager - stylesheet library

        1: clean-letter-14.ily (Abjad)
        2: clean-letter-16.ily (Abjad)
        3: rhythm-letter-16.ily (Abjad)
        4: time-signature-context.ily (Abjad)
        5: baca-letter-14.ily (Bača)
        6: red-example-score-stylesheet.ily (Red Example Score)
        7: gebiete-miscellaneous.ily (Gebiete)
        8: meters.ily (Manifolds)
        9: traiettorie-header.ily (Traiettorie inargentate)
        10: traiettorie-layout.ily (Traiettorie inargentate)
        11: traiettorie-miscellaneous.ily (Traiettorie inargentate)
        12: traiettorie-paper.ily (Traiettorie inargentate)

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

    > hls

    6 storehouses visible:

    /Users/trevorbaca/Documents/abjad/abjad/stylesheets
    /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/stylesheets
    /Users/trevorbaca/Documents/baca/score_manager_library/stylesheets
    /Users/trevorbaca/Documents/scores/gebiete/stylesheets
    /Users/trevorbaca/Documents/scores/mannigfaltigkeiten/stylesheets
    /Users/trevorbaca/Documents/scores/traiettorie/stylesheets

    >