Core infrastructure for InstrumentedNode

We want to reuse the functionality of InstrumentedNodes across environments. The different environments will have specific solutions for how commands are transmitted. Once a node receives them, a central infrastructure should be in place that provides an API for all commands. This component takes the commands and forwards them to the component that implements them. We could use the `NotificationEngine` to implement this.

For example, this API should provide a method to enforce branching. If a command to start branching is received (e.g., by a direct call in Turtle or via HTTP), the method is called and the command is forwarded to the component that controls branching (probably an extension of the EventCreator module).

Start by reviewing the NotificationEngine and EventCreator module references in the issue, then trace how InstrumentedNodes receive commands across environments. Done means a central command API is defined and commands such as branching are forwarded to their implementing components.

Written by the indexing model from the issue text.