Update title for discussions and announcements

Fixes: CNVS-12809

The title on both assignments and announcements
now better represent the pages that they belong to.

Test-Plan:
  - Create a course and navigate to that course
  - Navigate to announcements
  - Once there, create an announcement
  - Inspect page, and Title should be "New Announcement"

  - Likewise for Editing an announcement, and
      creating and edition a discussion post, Title
      should be "Edit Announcement", "New Discussion Topic"
      and "Edit Discussion Topic" respectively.

Change-Id: I94006f061f5535bd1c66e93c6d2af3bfcf75c4b7
Reviewed-on: https://gerrit.instructure.com/34237
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Drew Bowman <dbowman@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Jayce Higgins <jhiggins@instructure.com>