Added 'duplicate' menu option

For now duplicates next to original document in the same collection

app/menus/DocumentMenu.js

@@ -36,6 +36,10 @@ class DocumentMenu extends React.Component<Props> {
     this.props.history.push(documentMoveUrl(this.props.document));
   };
 
+  handleDuplicate = async (ev: SyntheticEvent<*>) => {
+    this.props.document.duplicate();
+  };
+
   handlePin = (ev: SyntheticEvent<*>) => {
     this.props.document.pin();
   };
@@ -100,6 +104,9 @@ class DocumentMenu extends React.Component<Props> {
             >
               New child document
             </DropdownMenuItem>
+            <DropdownMenuItem onClick={this.handleDuplicate}>
+              Duplicate
+            </DropdownMenuItem>
             <DropdownMenuItem onClick={this.handleMove}>Move…</DropdownMenuItem>
           </React.Fragment>
         )}