[qtdemux] parse support for clean aperture

Submitted by Philippe Normand @philn

Link to original bug (#596571)

Description

The mov file in https://bugzilla.gnome.org/show_bug.cgi?id=596319 has clean aperture data too. It doesn't seem to be correctly parsed by qtdemux.

Extract of qtdump:

 clean aperture (clap)  
   cleanApertureWidthN 41472  
   cleanApertureWidthD 59  
   cleanApertureHeightN 576  
   cleanApertureHeightD 1  
   horizOffN 0  
   horizOffD 1  
   vertOffN 0  
   vertOffD 1