The TrackidModel takes a TrackidSet and presents it as a Gio.ListModel
that maps trackids into Track objects. Tracks can be found by value
using the bisect() function, which sorts the trackids by number by
default (this can be changed by overriding the do_get_sort_key()
function).
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>
