Constructs an object that reflects the structure of an App Group Model
@method constructAppGroupModel
@param id                unique key of group
@param lastUpdated       timestamp when app group was last updated
@param priority          toggles the assignment between user or group scope
@param links             discoverable resources related to the app group
@returns {}              the AppGroupModel object
function constructAppGroupModel(id, lastUpdated, priority, links) {
    var model = {};
    if(id) model.id = id;
    if(lastUpdated) model.lastUpdated = lastUpdated;
    if(priority) model.priority = priority;
    if(links) model.links = links;

    return model;
}