Improved (new) user experience.

Statement of problem: there's an edge case where the composer applies a view
and then creates a new asset. What should happen when the composer creates an
asset that would be hidden by the view?

This commit implements the solution in which all views are cleared after asset
creation. This means that the composer will always be able to see any asset she
or he just created.

Example:

    Abjad IDE - scores

       1: Aracılık (2014)
       2: Betörung (2012)
       3: Blue Example Score (2013)
       4: Čáry (2006)
       5: Chrysanthemums (1995)
       6: Étude Example Score (2013)
       7: Gebiete (2013)
       8: L'archipel du corps (2011)
       9: Las manos mágicas
      10: Lidércfény (2008)
      11: L'imaginare (2010)
      12: Manifolds (2013)
      13: Mon seul désir (2009)
      14: Poème récursif (2005)
      15: Red Example Score (2013)
      16: Red Shift Hijinks (2005)
      17: Sekka (2007)
      18: Tack (1996)
      19: Territoires
      20: Traiettorie inargentate (2013)
      21: Zeit (1998)

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

    > vap

    Abjad IDE

      Select view to apply:

       1: bača
       2: cary
       3: examples

    > 3

    Abjad IDE - scores (examples)

       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)

    > new
    Enter score package name> example score

    Abjad IDE - scores

       1: Aracılık (2014)
       2: Betörung (2012)
       3: Blue Example Score (2013)
       4: Čáry (2006)
       5: Chrysanthemums (1995)
       6: Étude Example Score (2013)
       7: Gebiete (2013)
       8: L'archipel du corps (2011)
       9: Las manos mágicas
      10: Lidércfény (2008)
      11: L'imaginare (2010)
      12: Manifolds (2013)
      13: Mon seul désir (2009)
      14: Poème récursif (2005)
      15: Red Example Score (2013)
      16: Red Shift Hijinks (2005)
      17: Sekka (2007)
      18: Tack (1996)
      19: Territoires
      20: Traiettorie inargentate (2013)
      21: Zeit (1998)
      22: example_score

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

    >