Make the module sidebar available independent of scroll

[akoppela]

trafficstars

As a user I would like to have easy access to Module Docs sidebar with links and search bar. Now if the description is long module docs links and search bar stays on top. It makes it difficult to scroll back to top.

There are at least two solutions:

• Add scroll to top link.
• Split module docs sidebar with description section. So it can have it's own scroll bar.

Probably scroll to top is the easiest way to do.

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.