Fix the autoaligner to use the new waveforms cache generator and GES Assets
Submitted by Jeff F.T.
We had a working automatic clip alignment feature in 0.15.x, which used Pitivi's audio waveforms processing module... however, this module has been replaced by a faster, better, stronger (more precise) module that happens to have a part of it written in C for performance (see "pitivi/coptimizations/renderer.c" and the way we use it in pitivi/timeline/previewers.py).
We need to port autoaligner.py to it, and also to use GES Assets (that part should be trivial).
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=708401