loading the child asynchronously from server

@fritz-c thanks for the very great component. We want to know how we can load the children's child asynchronously when the `expand` button is clicked.

Initially, we want to send the UI just the first depth and as the user clicks on the expansion button we want to pull more data.
We sending column `hasChildren` boolean for a placeholder for asynchronous data. So when the expansion is clicked it will pull additional node data from the backend.
Let me know what I need to tweak to get there.
```
treeData: [
{
"title": "development",
"isDirectory": true,
"hasChildren": true,
"children": [
{
"title": "examples",
"isDirectory": true,
"hasChildren": true,
},
{
"title": "private",
"isDirectory": true,
"hasChildren": true,
},
{
"title": "projects",
"isDirectory": true,
"hasChildren": true,
}
]
}
],
```