Prevent scroll from bubbling up to GitHub page.

When Octotree has a scroll in a repository:

Once the top/bottom of the list is reached in Octotree after scrolling, the parent (GitHub page) starts scrolling and the current position in the open file is lost (as it scrolls), which is frustrating.
- The scroll/wheel event should be stopped from bubbling to the GitHub page.
It would be nice to have a (thin) scrollbar.
- If the scrolling of the GitHub page is intentional, then at least adding a scrollbar would be nice so that the user knows that they have reached the beginning/end of the list.

This is the environment used in the above video.

ovity / octotree