Enforce naming conventions

[RunDevelopment]

This PR enforces the following naming conventions:

1. The file name of a node is the node name.
2. The function name of a node is the node name + _node.
3. The function name of a helper node is iterator_helper_ + node name + _node.

I have chosen those naming conventions (especially for iterator helpers), because they can be automatically fixed. In fact, I did not enforce them by hand. I added some code to register that automatically enforces them by changing the source files themselves. However, I still need to think of a good API for this, so it will be added in a later PR.