Fix answer notification alignment to bottom
This PR changes the alignment of answer submission notification. Currently the notification is aligned vertically centred if not in viewport. This behaviour was observed in Chrome browser (87+). The alignment was correct when tested on Mozilla Firefox (86.0)
*JIRA Tickets*: [BB-3828](https://tasks.opencraft.com/browse/BB-3828)
*Sandbox URL*: TBD
1. Get the master devstack running
2. Sign in to LMS
3. Open Exam section of Demo Course.
4. Answer questions and click on Submit button.
5. Verify that the notification is scrolled to the *centre* of the viewport when not in viewport.
6. With notification in centre of viewport, submit another answer.
7. Verify that page does not scroll.
8. Now checkout to this branch and perform the same tests after restarting the LMS server
a. Verify that the notification is scrolled to the *bottom* of the viewport when not in viewport.
b. With notification in viewport, submit another answer
c. Verify that the page does not scroll.
[ ] @viadanna
[ ] @Agrendalath
[ ] edx-reviewer