Implement webworker for save operation + Limit the history size (#29)

- Implement webworker for save operation
- Limit the history size

Reviewed-on: https://git.siklos-chaneru.duckdns.org/Siklos/svg-layout-designer-react/pulls/29

src/workers/worker.js

@@ -0,0 +1,25 @@
+onmessage = (e) => {
+  const data = JSON.stringify(e.data.editorState, getCircularReplacer(), e.data.spaces);
+  postMessage(data);
+};
+
+const getCircularReplacer = () => {
+  const seen = new WeakSet();
+  return (key, value) => {
+    if (key === 'parent') {
+      return;
+    }
+
+    if (key === 'SelectedContainer') {
+      return;
+    }
+
+    if (typeof value === 'object' && value !== null) {
+      if (seen.has(value)) {
+        return;
+      }
+      seen.add(value);
+    }
+    return value;
+  };
+};