FLINK-990 Scala API: Compiler Hints are not forwarded

Added constant fields and combinable annotations forwarding to Scala API. The problem is that annotations information is not available when the Operators are created. Thus, we need a operator translation similar to the new Java API which triggers an update of the respective semantic information.  Furthermore, the Scala generated annotations are appended to the operator class, whereas the udf is checked for annotations. That's why Scala's combinableReduce operation does not generate a combinable operator.