function existsConnection(source, target) {
  return some(source.outgoing, function(c) {
    return c.target === target;
  });
}
Creates a new shape.

@param {Object} context
@param {Partial<Shape>} context.shape The new shape.
@param {Element} context.source The element to which to append the new shape to.
@param {Parent} context.parent The parent.
@param {Point} context.position The position at which to create the new shape.