Cleaned up Wrangler._select_storehouse_path().

Reimplemented method around Selector instead of Menu. This eliminates the
while-true loop necessary to treat the menu like a selector.
Harmonized StylesheetWrangler and MakerModuleWrangler make methods.

Both are now single statement wrappers around Wrangler._make_file().
Cleaned up Manager.remove().
Extended main menu.

Example:

    Score manager - example scores

        1: Blue Example Score (2013)
        2: Étude Example Score (2013)
        3: Red Example Score (2013)

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

    > q

The (cp), (rm) and (ren) commands are new.

The (cp), (rm) and (ren) commands will be implemented in future commits.
Changed abjad_score_packages=None to example_score_packages=None.
Alphabetized keywords.
Extended Selector._run().

Selector._run() now swallows lone return.
Improved StylesheetWrangler.make_stylesheet() user experience.

The method now fast-tracks in-score stylesheet creation to the current
stylesheet directory; no need for the user to (redundantly) choose the current
stylesheet directory by hand.
Updated TODO.
Extended StylesheetWrangler (rm) command.

You can now remove multiple with range selection.

Example: Consider the following score. We want to remove the orange, purple and
white stylesheets. We can do this with a single command.

The menu prompts us to type a special confirmation string because we are
removing more than one styleshseet at one time:

    Red Example Score (2013) - stylesheets

        1: orange-stylesheet.ily
        2: purple-stylesheet.ily
        3: red-example-score-stylesheet.ily
        4: white-stylesheet.ily

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

    > rm

    Enter stylesheets to remove> 1-2, 4

    Type 'remove 3' to proceed> remove 3

    Red Example Score (2013) - stylesheets

        1: red-example-score-stylesheet.ily

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

    >

The same behavior will be ported to all wranglers.
Updated TODO.
Made Wrangler._remove() private.

MODEL: the inheritance model is that Wrangler._remove() is private and is the
workhorse method that does everything. Then the following methods ...

    * BuildFileWrangler.remove_build_file()
    * DistributionFileWrangler.remove_distribution_file()
    * MakerModuleWrangler.remove_maker_module()
    * MaterialPackageWrangler.remove_material_package()
    * ScorePackageWrangler.remove_score_package()
    * SegmentPackageWrangler.remove_segment_package()
    * StylesheetWrangler.remove_stylesheet()

... are single-statement wrappers around the private method in the baseclass.

This is true for StylesheetWrangler.remove_stylesheet() and
MakerModuleWrangler.remove_make_module() as of this commit.

The pattern will be extended to the other wranglers in coming commits.
Changed Wrangler._initalize_asset_manager() to Wrangler._initialize_manager().
Cleaned up Wrangler._rename().

Method is now implemented in parallel to Wrangler._remove().
Cleaned up Wrangler._rename_asset() and Wrangler._remove_asset().

Factored out asset-selection logic from both methods.
Implemented MenuSection.__getitem__().

You can now iterate menu sections directly.
Removed (p) from ScorePackageManager main menu.

The 'setup' (p) command now appears only in the output of (?).
Wrote MaterialPackageWrangler menu tests.

Tests ensure that score annotation is shown when listing materials outside of
score; tests also ensure that score annotation is not shown when listing
materials inside score.
Removed global (p) navigation.

If you want to manage score setup you should use (p) at the ScorePackageManager
main menu.

Previously you could use (p) anywhere inside a score. This commit removes that
extra navigation affordance.

This means that these six global navigation commands ...

    build (u)
    distribution (d)
    makers (k)
    materials (m)
    segments (g)
    stylesheets (y)

... now work inside scores and outside of scores equally.

So use (y) anytime anywhere. But use (p) only at ScorePackageManager main menu.
Updated TODO.