Implement way split in crossings

[Krakonos]

Currently, when two ways share a node as their inner node, the way cannot be split easily. This is bad when you are making a relation needing the split. This should be fairly straightforward to fix.

(Note: you can split the way if you select both the node and the way, but just a node should result in splitting all ways sharing it.)

[Krakonos]

This can actually be done if you select the Node AND Way you want to split. I'm switching this to documentation request.