Remove explicit only interface for IEnumerable, and IList for JArray 

Although for pretty much all standard usages, having an explicit IEnumerable interface is not an issue.  

However, there are some dlr issues with this, and by removing this limitation it allows dynamic JObjects to be wrapped with an Interface using [ImpromptuInterface](https://code.google.com/p/impromptu-interface/) similar to what Mark Rendle does with [HOWTO: Dial up the static on Simple.Data](http://blog.markrendle.net/2012/10/12/howto-dial-up-the-static-on-simple-data/)

Also referenced on [StackOverflow](http://stackoverflow.com/questions/15873136/custom-impromptuobject)