Allow objects for tree resources

[mcweba]

The current implementation of the editor allows the following structure of tree resources only:

{
    "resources": [
        "resource_1",
        "resource_2",
        "resource_3"
    ]
}

This structure contains an array containing the names of the resources as string.

To be more flexible, the editor should also allow the following structure:

{
    "resources": [
        {
            "name": "resource_1"
        }
    ]
}

This structure contains an array containing objects having string name properties. These objects could contain additional properties which could be used in the editor in the future.