Extend the listener mixin to provide "initial" data

[spoike]

Add the possibility to fetch initial data from a data store to a React component. This needs a change to the ListenerMixin's listenTo method and in the store implementation as well.

Motivating Example

var aStore = Reflux.createStore({
    init: function() {
        this.listenTo(anAction, function() {
            this.trigger('not initial data anymore');
        });
    }
    getInitialData: function() {
        return "the initial data";
         // is used by Listenermixin if a component wants initial data 
    }
});

var Component = React.createClass({
    mixins: [Reflux.ListenerMixin],
    getInitialState: function() {
        return {}; // <-- impossible to know the state if stores aren't initialized yet
    },
    componentDidMount: function() {
        this.listenTo(aStore, changeCallback, changeCallback);
            // will call changeCallback twice, during store change and 
            // when the store has initialized
            // third callback should be optional
    },
    changeCallback: function(data) {
        console.log(data);
        this.setState({
            data: data
        });
    }
});

In the example, before invoking the anAction the component should be able to set the state with "the initial data" fetched from the store's getInitialData method. When invoking the anAction the component should be able to set the state with "not initial data anymore" fetched from the change event.

Thoughts?

[KyleAMathews]

Interesting. Could getInitialData return a promise? That might be useful for server fetching. Actions are "held" until the promise is returned.

[spoike]

Probably should rename it to get "default" data. The point is more or less how to handle initialization of components, well before data comes in.

[spoike]

Closing issue as it is merged in #46 and #49