feat(controls): extendable controls via control button comp closes #1030

src/additional-components/index.ts

@@ -2,6 +2,6 @@
 // but the user can add them as children of a React Flow component
 
 export { default as MiniMap } from './MiniMap';
-export { default as Controls } from './Controls';
+export { default as Controls, ControlButton } from './Controls';
 export { default as Background } from './Background';
 export { default as ReactFlowProvider } from './ReactFlowProvider';