Exit drop down menu by clicking elsewhere

[JoshuaKissel]

Is this a BUG REPORT or FEATURE REQUEST?:
feature

What happened:
When drop down menus are active the only way to exit the drop down and stay on the same page is to re-click the menu header (aka the "parent"). This means that multiple drop down menus can be open at the same time.
What you expected to happen:
Feature: when clicking outside the open drop down menu the menu should close.
How to reproduce it (as minimally and precisely as possible):
Add a drop down menu, then open the menu.
Anything else we need to know?:
Related to issue #825
Environment:

• Syna Theme version: v0.17.3
• Hugo version: v0.74.3/extended windows/amd64
• Others: