refactor trackfilter.

refactor trackfilter.

use std::sort, stable_sort instead of qsort.
use QList instead of malloc'd arrays.
minimize the use of duplicated information (track_ct, track_pts, timeless_pts
first_time, last_time), and maintain the remaining
duplicated information (track_list, a possible sorted version of my_track_head).
use auto some more.
eliminate some redundant casting.
eliminate atoi.