Sidebar styling updates

Problem

Headings in the job sidebar are currently misstyled. An example of this is clear when you have a job which is triggered. The "Trigger section" header is far bigger than even the job's own name.

Also, there are various other styling updates that can be done, such as updating color, font-weight, padding (text vs buttons)

Further information

Created because of meeting for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23518#note_121973296

Solution

Notes:

• Merge request row in sidebar is not needed as it already referenced in the commit section screenshot example

What does success look like, and how can we measure that?

Job sidebar has a clearer information hierarchy where the font-sizes, weights, and color make sense vs the information they represent

Links / references