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
Would it be possible to do the majority of the work server-side? Hardcode the XML array into the PHP file, and on the JS side we should only have to do `$.post(courses)`. (PHP can handle JSON).

I'm not too fond of having an endpoint which you can throw any data at and get a download. Doesn't seem vulnerable to CSRF or anything, but just in case ;)