Make GitLab accessible on HD (720p) screens

Summary

GitLab page content size is too large to use on 720p screens.

This resolution that's still widely used on desktops as most surveys;

• https://www.w3counter.com/globalstats.php
• http://gs.statcounter.com/screen-resolution-stats

This issue is created based feedback we received on HN https://news.ycombinator.com/item?id=17590469