Improve ICS downloads for MAC

[Sander Roosendaal]

Both my Safari and Firefox browsers (Mac) now view the file as an HTML file and save it accordingly (see screenshot attached, from Firefox). No .txt extension appears, but now it is .html. As before, if I rename the file to delete the .html suffix, it imports into my calendar just fine.

[Sander Roosendaal]

Trying setting 'Content-Type' to 'application/octet-stream'

[Sander Roosendaal]

Reports from the field indicate that this is working now