Upgrade bootstrap from 4.3.1 to 4.6.0 before major upgrade

[Doris Tam]

To receive all security updates, upgrade to latest minor point Bootstrap 4

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/11828

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/11829

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/11828
Committed: https://git.mahara.org/mahara/mahara/commit/f5fb2ec2eee32e8fefcfd36e48ce0cb9dadeb223
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit f5fb2ec2eee32e8fefcfd36e48ce0cb9dadeb223
Author: Doris Tam <email address hidden>
Date: Thu Jun 10 21:45:18 2021 +1200

Bug 1931557: Upgrade Bootstrap to 4.6.0

Updating sass / js files

Change-Id: I8ff1072629e33763b7ea831f3dde189ac94808ac

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/11829
Committed: https://git.mahara.org/mahara/mahara/commit/0fada8bd76ebac50a250ea9037c32210f1e6f16b
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 0fada8bd76ebac50a250ea9037c32210f1e6f16b
Author: Robert Lyon <email address hidden>
Date: Mon Jun 14 09:28:03 2021 +1200

Bug 1931557: Upgrade Bootstrap to 4.6.0 - adjustments

Had to add !optional to _grid.scss as our $grid-breakpoints for xs is 0 which breaks the normal process.

Change-Id: I4cc1ed4a92217b238701334b79b169d7b95d60a0
Signed-off-by: Robert Lyon <email address hidden>