Wrote StylesheetWrangler.remove_views() tests. MODEL.

MODEL: all remove commands will operate on ranges. This means that all remove
commands will allow the composer to remove multiple items at one time.

You can now remove multiple views at one time.

Example:

Here there are four views defined:

    Score manager - stylesheet library

        1: baca-letter-14.ily (Bača)
        2: clean-letter-14.ily (Abjad)
        3: clean-letter-16.ily (Abjad)
        4: gebiete-miscellaneous.ily (Gebiete)
        5: meters.ily (Manifolds)
        6: red-example-score-stylesheet.ily (Red Example Score)
        7: rhythm-letter-16.ily (Abjad)
        8: time-signature-context.ily (Abjad)
        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)

    > vls

    4 views found:
    apple
    banana
    cherry
    durian

    >

Here we remove three of the four views at one time:

    Score manager - stylesheet library

        1: baca-letter-14.ily (Bača)
        2: clean-letter-14.ily (Abjad)
        3: clean-letter-16.ily (Abjad)
        4: gebiete-miscellaneous.ily (Gebiete)
        5: meters.ily (Manifolds)
        6: red-example-score-stylesheet.ily (Red Example Score)
        7: rhythm-letter-16.ily (Abjad)
        8: time-signature-context.ily (Abjad)
        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)

    > vrm

    Score manager - stylesheet library - select view(s) to remove:

        1: apple
        2: banana
        3: cherry
        4: durian

    > 2-4

    View inventory written to disk.

    Score manager - stylesheet library

        1: baca-letter-14.ily (Bača)
        2: clean-letter-14.ily (Abjad)
        3: clean-letter-16.ily (Abjad)
        4: gebiete-miscellaneous.ily (Gebiete)
        5: meters.ily (Manifolds)
        6: red-example-score-stylesheet.ily (Red Example Score)
        7: rhythm-letter-16.ily (Abjad)
        8: time-signature-context.ily (Abjad)
        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)

    > vls

    1 view found:
    apple

    >