[Request] midscroll

**What software are you requesting to be packaged?**
https://github.com/gnhen/midscroll
https://www.reddit.com/r/linux/comments/1v503xk/midscroll_windowsstyle_middleclick_autoscroll_for/

**Describe the motivation**
Middle-click scroll is a common request for Windows users moving to Linux.

**Additional context**

