Reimplement ``e.dataTransfer.dropEffect``.

I ran into several problems with accessing the `effectAllowed` attribute. 

Accessing this attribute is not possible in IE (<permission denied>). 

According to [this msdn source](http://msdn.microsoft.com/en-us/library/ms533743(VS.85).aspx) the attribute has to be set in the `ondragstart` event. 

I tried this by adding the following code:

```javascript
        qq.attach(document, 'dragstart', function(e){
            e.dataTransfer.effectAllowed = 'move';
        });
```

But the event will not be triggered. 

I tried to fix it before for IE 10 by adding checks -> https://github.com/collective/collective.quickupload/commit/48dae65379d35057d61310fd3dfbfad6b719dbc9

Well, of course IE 11 delivers a different header, 'MSIE' is no longer in there, also jQuery 1.7.2 thinks that it is a mozilla firefox (`$.browser.mozilla` returns true). 


After some :rage4: I decided to remove my IE10 fix commit and also the parts where `effectAllowed` is used. 
It still works and I cannot see any difference...

In my case the DnD upload works with:
- IE 10
- IE 11
- Chrome ~37
- Safari 7 (The amount of dragged files is always 0, but this is no a issue of this change)
- Firefox 32

Please review this, because I'm still not sure what I'm doing here :smile:

cc // @tdesvenain @macadames