Improve primary action and cancel button pattern

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

Summary

Add and Cancel buttons should not be so far apart, but rather adjacent with primary Add emphasized and secondary Cancel de-emphasized.

Steps to reproduce

Go to an issue page and click the Add Related Issue button.

Relevant logs and/or screenshots

Screen_Shot_2019-05-21_at_3.03.06_PM

Edited by 🤖 GitLab Bot 🤖