Resolve "Tooltip for pinning sidebar"

## What does this MR do?
Adds tooltip to show whether sidebar is pinned/unpinned

## What are the relevant issue numbers?
Closes #18743 

## Screenshots (if relevant)
![Screen_Shot_2016-06-17_at_12.14.25_PM](/uploads/162f52084a770012cdc621122acd6c6c/Screen_Shot_2016-06-17_at_12.14.25_PM.png)
![Screen_Shot_2016-06-17_at_12.14.35_PM](/uploads/d9296720aeada972441f48d9a3d2f7f8/Screen_Shot_2016-06-17_at_12.14.35_PM.png)

See merge request !4759