Toggle panel columns

When panels are displayed on the right and left of the page, a toggle appears on hover. Interacting with the toggle will either hide or show the panel column. Hiding a panel column will also reset the preference for this column width. The state of the columns is synchronized across tabs. This preference is stored at the browser level, meaning that navigating to a new page ont he same wiki will not lose this preference, but moving to another machine will. Read more about the panel layout and how this new toggle interacts with the existing system.