Clean up `abjad.illustrators.components()`

[trevorbaca]

Add an explicit abjad.Voice context to the output created by abjad.illustrators.components().

EXAMPLE:

def main():
    components = [abjad.Note("c'4")]
    lilypond_file = abjad.illustrators.components(components)
    string = abjad.lilypond(lilypond_file["Score"])
    print(string)

OLD:

\context Score = "Score"
<<
    \context Staff = "Staff"
    {
        \time 1/4
        c'4
    }
>>

NEW:

\context Score = "Score"
<<
    \context Staff = "Staff"
    {
        \context Voice = "Voice"
        {
            \time 1/4
            c'4
        }
    }
>>