The working copy menu as well as all the buttons and notification icons in the top right corner of the Scrivito panel, except the page menu, have moved to the sidebar. (The page menu icon has been redesigned, too, by the way.)
To give you full control over the amount of space available for editing content, the sidebar can be minimized, left open, or hidden together with the Scrivito top panel. In the minimized state, there are four main buttons each of which represents a distinct set of functions: the Content Browser, working copies, notifications, and display sizes. The Content Browser is opened directly, but clicking one of the other buttons opens the sidebar, revealing the functions included in the corresponding set. Clicking the button once more minimizes the sidebar again.