Added id options for track initialisation data

The id option string in assistantPerformer.html now contains volume and pitchWheelDeviation values
which are sent to each track at the beginning of
each performance.
The id option's separator is now a comma separated
by whitespace ad lib.
The ti.volume values are currently simply overridden
by a po.pressure.minimum value. But this will change.
TODO: the ti.volume values should represent the
maximum volumes in both assisted and non-assisted
performances. Is is correct to initialise the tracks with
po.pressure.minimum, but when pressure values are
sent during a live performance, they should be
scaled per track between po.pressure.minimum and
the track's maximum volume (found in ti.volumes).