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

tsconfig.json

@@ -16,7 +16,7 @@
     "noEmit": true,
     "jsx": "react-jsx"
   },
-  "include": ["src"],
+  "include": ["src", "src/workers"],
   "exclude": ["test-server"],
   "references": [{ "path": "./tsconfig.node.json" }]
 }