Specify edge behavior in the JSON file

[kohlhase]

cc: @maxgrapp
WE currently have an edge type in the json. Currently the algorithms hard-code

• "include" to be hierarchy-inducing
• all others to be ignored in layout

We should have an abstract behavioral description categories, i.e. somehting like

• hierarchic
• directed
• shortenme(maybe with a strengh parameter)
• ignoreme
• undirected
  these could act like CSS classes that guide the general layout algorithms and thus decouple things more.

[tkw1536]

/cc @rappatoni

[richardmarcus]

should also discuss graph types, e.g., "archivegraph"