Refactor to abstract MOOC and Coursera
Back to .NET 4.0. Using 7Zip instead of .NET 4.5 built-in.
Small refactor of login... not working
Got file name from header.
Added coursera option

Future will allow for other MOOC websites.
Also sanitize the filename.
Merge remote-tracking branch 'origin/ExtractCoursera'

Conflicts:
	courseradownloader/CourseraDownloader.cs