Streaming Scala API

This PR contains the commits for the Scala api for Flink Streaming. Most functionality is already implemented and I think it is ready to merge after maybe some slight refactoring.

I would appreciate if someone with more scala experience could look it through, that code works but it might not be very pretty everywhere.

Also If anyone can please run a scala formatter on the code since it seems impossible to get line wrapping settings in eclipse so I had to break the lines manually to make travis pass.

What's missing:
- groupBy("field") operator for case classes. The streaming api currently doesn't use the comparators but instead it extracts the keys from elements. I need to figure this out for case classes.
- Connected data stream functionality, I will add this soon. This is trivial.
- Proper scala code-style formatting, see above
- I am not sure about the package structure, any comments on how I did it?

Feel free to play around and test the features, I am sure that there will be bugs to fix :)