Functions which don't have grouping information is grouped as Actions

@benglin, please review.
I would like to make a suggestion to get rid of ```nodeGroups``` data member in this class, please let me know what do you think about the following (with a faster ```switch-case``` statement):

```cs
    // If 'index' is '-1', then the whole 'category' will be used as-is.
    switch (category.Substring(index + 1))
    {
        case "Actions":
        case "Create":
        case "Query":
            return category; // Group name is already known.
            
        default: // Defaulting to "Actions" group if not defined.
            return category + CATEGORY_DELIMITER + defaultGroup;
    }
```