add module navigation to react discussions
add module navigation to react discussions

fixes VICE-1568
flag=react_discussions_post

Test Plan:
- Create a module and add a couple discussions to it
- Publish the module
- Navigate to the discussion through the module
- You should see the next/previous module navigation buttons
  and they should work

Change-Id: Ic39628bf5d07c6349bb6dc15514b8fd44fbb9354
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/269407
Product-Review: Allison Pittler <2a5a246549b8bd80f0da3da80141043abdbaa521@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Caleb Guanzon <54fa1f30d451e4f3c341a8f3c47c9215fd0be9c6@instructure.com>
QA-Review: Caleb Guanzon <54fa1f30d451e4f3c341a8f3c47c9215fd0be9c6@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms