Add user calendar, with all course offerings for a user

Problem/Motivation

A teacher may be involved in a number of course offerings, and it would be nice to have a collected schedule for those.

Proposed resolution

Add a calendar on the user page, showing either all course offerings a user has created, or all course offerings a user has marked as favourites.

Remaining tasks

Do the stuff.
Evaluate.
Iterate.

User interface changes

(as described above)

API changes

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