Linking Nodes - 1:1 relation

**Is your feature request related to a problem? Please describe.**
I'd like to use this awesome library but I didn't find the option to make 1:1 relation of links
Now you can connect 1 node with n other nodes.

**Describe the solution you'd like**
When a node is connected with another one, the port should be disabled (so that it doesn’t connect with another node) until the blocks are disconnected.