Link creation with support for mobile safari

[JannikStreek]

Links inside a foreign object element seem not to work on mobile safari. Therefore, the link creation strategy has to leverage native svg link elements instead of making use of foreign object. This requires bigger changes in the underlying map lib. The alternative would be to add an onclick element, but this leaves room for possible XSS exploits.

Using native svg links means, that not these node are not editable anymore.

[JannikStreek]

Alternative idea: Link is not clickable directly. When the node is displayed, show a link symbol next to the node which is clickable. This also has the advantage not to accidentally click on a link if you wanted to move the node.