fix: content shift when y-scrollbar disappears

Created by: Tirokk

Authored by rbeer Feb 24, 2020 Closed Mar 5, 2020

---

🍰 Pullrequest

This change

1. calculates the width of the vertical scrollbar (px-value)
2. sets px-value as padding-right to .main-navigation and body

thus preventing the page's content from shifting when filling up space that the disappearing scrollbar leaves behind.

Issues

• fixes #2607 (closed)
• relates #2564 (closed)

Todo

• None