Feature: Add relations

## Description

The idea is to link two **Nodes** with a **Relation** between them, so given two nodes in the canvas, you can drag from one node to another to create a relation.

## Behaviors
* [ ] draw relations on canvas
* [ ] create relation by dragging from one node to another

## Tasks
* [ ] fix node refences in relation object
* [ ] fix node finder in relation object
* [ ] extract relation object
* [ ] return relation objects instead of relation data in `scope.relations`
* [ ] add text to relations