gb2 total column in front

fixes CNVS-4373

* fixes tooltip showing when total col is moved
* changes to have consistent border on cells
* changes .sass to .scss file so we know it's actively worked on

test plan:

- load up the gradebook page
- move total column to first and make sure tooltip works on hover
- make sure dotted line border appears on table cells (see comments for screenshots)

Change-Id: I7927ec37658f938bbfdb3e87c12f7da5014aeaa1
Reviewed-on: https://gerrit.instructure.com/37393
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>