Let the user create more bendpoints for structural links

[vainolo]

Currently structural links are connected to and from elements using Manhattan routers. A better way to connect them would be to create special bendpoint routers which allow the user to create new perpendicular benpoints like this:

---

thing1

  -------
          |
         / \
         ---
          |            ---------
          ----------| thing2 |
                        ---------

Solution can probably be implemented using a limited bendpoint connection router

[vainolo]

Tried implemented by chaning the edit policy wich creates the links to limit how they are created. This became difficult since all locations must me calculated manually... and there are a lot of dependencies. Postponing for later.

[vainolo]

Cancelled. I have decided that all layout will be automatic.