refactor Reflux.all

[krawaller]

This PR refactors the code for Reflux.all.

I found the prior implementation, returning a hacked action, to be a bit dangerous. What we get back is both a listener and a publisher, which means it is really a store! By implementing it as such instead we get shorter code, and we can get rid of the extra hasListener method which was needed earlier since the action was moonlighting as a listener.

As a bonus, by using ListenerMethods.listenTo instead of directly calling PublisherMethods.listen, we get an object which can clean up itself.

Less LOC:s, less debt and headache waiting to happen.

There is an ever so slight API breakage as we no longer get back a functor, but I doubt it was ever used in such a way.

[krawaller]

Just realised that listenable aggregation is potentially useful not just for a publisher, so I abstracted out the functionality into ListenerMethods.listenToAggregate(...listenables,callback).

This means that Reflux.all is now just doing this:

var listenables = Array.prototype.slice.call(arguments);
return createStore({
    init: function(){
        this.listenToAggregate.apply(this,listenables.concat("trigger"));
    }
});