Jobs page scrollbar and centering

Observed on 9.3.0-pre b527f79d.

Plan of action

Scrollbar is to thin

This makes regular tasks a bit more difficult. I often grab the scrollbar to jump to the middle of the log because our build logs are big.

• make scrollbar 7px wide (same as chrome on mac default scrollbar width)

• center scrollbar on arrows

https://gitlab.com/gitlab-org/gitlab-ce/uploads/fede58de8824996f5f20d0ba02aaca36/image.png

Pipeline information is centered

Because of this, the page looks a bit weird.

• titlebar should stretch :)