Export as .ics(solves #10)

Added a button "Export as .ics"
Click takes data from elements with class 'used' and associates them
with time data from 'data.xml'
A .ics file is generated that is sent to 'download.php' which then
forces it as a file download upon browser
This is very inefficient, we're fetching the XML for every course. (Additionally, it just says "Class" instead of the course name, though that's a quick change)