Parameter for combination of section and lectures numbers added

Hi,

I've added a very simple parameter to include the section number in the final files.
I was trying to have a playlist with all play all the videos for a given module but there was no way of sorting them globally. This is possible with section and lecture numbers. 

For instance, "04_Factors.mp4" and "04_Normalisation.mp4" will become "01_04_Factors.mp4" and "02_04_Normalisation.mp4", so we know the factors lecture should be played first.

Regards,