Add opttion to position blocks at bottom of course page

[Jeremy Hopkins]

Related to #706

Add setting to move sidebar to bottom of course pages above footer. This would allow full width content in course pages.

This cannot be done with layout builder as sidbar is default region. We simply need to move this region to the bottom along the lines of the hidden region on the front page.

We need it to display 4 blocks wide to maintain reasonable presentation / use of space.

[Manoj Solanki]

After discussion with Jeremy, this will be done with a layout builder similar to that created for issue #706. This will allow for positioning block regions in the new layout if the new option to move sidebar to bottom (which will be done as part of this change) is selected.

[Manoj Solanki]

Fix #706 and #715. First check-in. To be tested on 3.3 and also code checker.

→ <<cset ebfc1c4b8b12>>

[Manoj Solanki]

Please test and merge for this and #706 on master-wip-mani. Thanks.