Issue 2617: simple chord inversions take 2 octaves

Issue 2617: simple chord inversions take 2 octaves

With this change, chord inversions transpose all notes following the
inversion from the original chord down along with the inversion, as long
as the result ends up below the root note of the uninverted chord.

So with \chordmode { c:11 } => < c' e' g' bes' d'' f'' >
we get \chordmode { c:11/e } => < e g bes c' d'' f'' >

In order to have the Chord_name_engraver reconstruct the correct
uninverted chord, all the additionally octavated note events are given
an octavation property like the inversion event itself.

[dak, 2014-07-10 11:27:09]

f/f -> <f a' c''>

[dak, 2014-07-10 13:27:16]

Adapt docs for inversion entry in chordmode