This will now show the last message that the user was part of in
the activity stream instead of the last message sent to anyone in
the parent conversation.
Fixes COMMS-1468
Test Plan:
* Have a course with at least one teacher and two students
* As the teacher, send a message to both students
* Go to student 1's dashboard and select the activity stream. Notice
the timestamp for the message
* Wait for 60 seconds
* As student 2, reply to the message (only reply to the teacher).
* If you have redis caching setup, flush the cache here by running
`redis-cli` in a terminal, then running `flushdb`
* As student 1, reload your dashboard and notice the timestamp for
the conversation hasn't been changed.
Change-Id: I51968966643f351faaf46bcdfce542ec77617039
Reviewed-on: https://gerrit.instructure.com/165893
Reviewed-by: Steven Burnett <sburnett@instructure.com>
QA-Review: Steven Burnett <sburnett@instructure.com>
Tested-by: Jenkins
Product-Review: Landon Gilbert-Bland <lbland@instructure.com>