calendar2: list favorite courses first

fixes CNVS-12108

test plan:
  * select some favorite courses and some non-favorite courses
  * open calendar2
  * verify that in the sidebar, your favorite courses are listed
      before your non-favorite courses

Change-Id: Ia5f9da19d487d87bf70514fbeae7d9c68c52eb39
Reviewed-on: https://gerrit.instructure.com/33265
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>