Accept node object from Router

Problem/Motivation

The NodeAuthlinkNodeForm form builder class is explicitly loading node objects instead of accepting it from Drupal's Routing system. This has the implication that other modules (e.g. entity_hierarchy) working on node routes are also getting a node id for the node route parameter instead of the node object. This is leading to fatal errors in some cases.

Steps to reproduce

1. Install node_authlink and entity_hierarchy modules.
2. Configure node_authlink for at least one content type.
3. Open a node of that content type and click the Authlink tab.
4. This should lead to a White-screen-of-death.

Proposed resolution

The attached patch fixes this issue while retaining the original behaviour. It uses parameter upcasting to achieve this.

Remaining tasks

More testing...