Return the HTML as an ext ics attribute for those few clients that
support it (Outlook), and return better-formatted plain text for all
other clients.
closes#9107
Also refactor a bit.
test plan: add assignment and calendar events to the calendar with
links, formatted text, etc in their descriptions. Export the calendar
feed. In Outlook, you'll see the full HTML of the event. In most other
clients, you'll see a plain-text version of the description, but it'll
be much better formatted than it was before.
Change-Id: I50af1c407483d84c65ca285cbf364b6a303e0379
Reviewed-on: https://gerrit.instructure.com/11891
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
b283bc3b87