Scala examples for Triangle Enumeration

Added first versions of the Scala examples for triangle enumeration.
The examples include:
- Annotation of edges with the corresponding vertex degrees (+ unique projection of vertexes and duplicate removal)
- Enumeration of triangles on edges with degrees.

The examples perform the same job as the corresponding Java versions. However, they use different strategies (joins instead of reduce in some places). Exactly following the Java strategies didn't work for a Scala novice ;-)
However, this might be changed later.