Added local_groups resource

A straight forward coding using [chef's group resource](http://docs.opscode.com/resource_group.html)
Tested successfully with the following chef-json input:

```json
{
    "run_list": "recipe[gecos_ws_mgmt::default]",
    "gecos_ws_mgmt": {
        "misc_mgmt": {
            "local_groups_res": {
                "groups_list":[
                    {
                        "group": "audio",
                        "users": ["vagrant"]
                    },
                    {
                        "group": "video",
                        "users": ["vagrant", "ami"]
                    }
                    // The following result in failure
                    // Uncomment to test
                    //,
                    //{
                    //    "group": "this_group_dont_exist",
                    //    "users": ["vagrant"]
                    //},
                    //{
                    //    "group": "floppy",
                    //    "users": ["this_user_dont_exist"]
                    //}
                ]
            }
        }
    }
}
```