Added an option to download the videos from the direct links in the case
they are available, (skipping youtube-dl).

It uses a really simple non sophisticated file retriever.
Merge remote-tracking branch 'shk3/master'

Conflicts:
	edx-dl.py
Added support for fun (french mooc)
Remmoved welcome message

The welcome message is not in the same field in the fun french mooc.
As it is not essential for the functionality of edx I removed it.