Implement container adding

src/SVG/Elements/Container.tsx

@@ -11,12 +11,18 @@ interface IContainerProps {
 }
 
 export class Container extends React.Component<IContainerProps> {
-  public render(): React.ReactNode {
-    const containersElements = this.props.children.map(child => child.render());
+  public static ContainerCount = 0;
 
+  componentWillUnMount() {
+  }
+
+  public render(): React.ReactNode {
+    Container.ContainerCount++;
+    const containersElements = this.props.children.map(child => child.render());
     return (
       <g
         transform={`translate(${this.props.x}, ${this.props.y})`}
+        key={`container-${Container.ContainerCount}`}
       >
         <rect
           width={this.props.width}