Code block copy icon hides content #980

Describe the bug
When using horizontal scrolling in code blocks, the copy icon hides the blocks content.

Steps To Reproduce
Steps to reproduce the behavior:

1. Create a single line code block with text long enough to require horizontal scrolling.
2. The copy icon hides the last few letters

Expected behavior
Attach the copy icon to the outside of code blocks, or make it only visible when hovering over a code block.

Screenshots

Your Configuration (please complete the following information):

• Exact BookStack Version (Found in settings): v0.23.2
• PHP Version: 7.0.30-0ubuntu0.16.04.1
• Hosting Method (Nginx/Apache/Docker): Apache/2.4.18