Grouping options overwrite the global configuration 

Grouping options overwrites the global configuration options causing side effects at the tests. The problem is that configuration.grouping is directly extended with the options instead extending an empty object ...


    group: function group(obj, options) { // array of observables or viewModel
 
        // var options = ko.utils.extend(configuration.grouping, options),
        var options = ko.utils.extend(ko.utils.extend({} ,configuration.grouping), options),
        ...
    }

This pull request fixes that and adds a tests for it.