Allow to set param index in params array with 'index' key

Also, if param key is not a string and param.name is nil, create param name from index and type.

Example usage:

```
params = plugin.manageParams {
    {
        name = "Length",
        type = "int",
    },
    {
        name = "Feedback",
        index = 2,
        type = "int",
        ....
    },
    {
        type = "int",
        index = 1,
        ...
    }
}
```

Would yield these parameters in the given order:

0. "Length"
1. "Param 1 (int)"
2. "Feedback"