Realize connection loops in diagram instead of text block

[tobolar]

In several models, vectorized connections are realized in the equation section by for-loops like:

  for i in 1:n loop
    connect(...);
  end for;

For models implemented graphically, such connections can't be recognized - they are only visible in source code. But generally, mixing of graphical and textual implementation shall be omited.

This PR shows a possible solution to work only in the diagram layer. In DiscretizedCrossFlowHEX, the JunctionN element is added to realize such inner loops.