Share EventEmitter among group of related actions.

**Work in progress**

-----

- [ ] Update readme

-----

`Reflux.createActions` creates an instance of `_.EventEmitter` for every element in a given array of unique action names. Such an array of action names should be assumed to share 'context' or namespace.

Added check if an action has already been created for the edge case of duplicate action names.
I wonder if it would be easier to let the namespace/context take care of action creation instead (since ´Namespace´ doesn't extend EventEmitter that much to the point that it is quite anemic):

```javascript
context = new Namespace();
actionOnContext = context.createAction();
```

That way `Reflux.createAction()` will instead create an action from a default context found on `Reflux.defaultContext` or something.