Bug Fix: start marker was not being set correctly in 1-voice scores.

The "set start marker" tool threw an exception in 1-voice scores, because the track indices were not being set properly when there was
only one track.
Also: The scores Study 2c3.1 and Study 3 sketch 1 have been updated.
There is now a link to their respective "About" file at the top of page 1,
and the cursor no longer changes to an I-beam when over SVG text.
New SVG page format

Uploaded new SVG files for Study 2c3.1 and Study 3 sketch 1.
In SVG files, when a chord "use"s a chord definition in the defs section,
the msDuration attribute is the actual duration of the chord in the score
at speed = 1. The msDurations of the basicChords inside the used chord
do not necessarily add up to this value.
When calculating the msDurations of moments, first the total duration of the basicChords is calculated, then the moment msDurations are
set (proportionally to the basicChord msDurations) so that their total
msDuration is equal to the chord's msDuration attribute.
The global speed option simply changes the way the chord's
msDuration attribute is used.
Bug Fix:  system.msDuration is now reset after clicking the Start
button.