Update some of our architectural constraints

[sbegaudeau]

While the project was started a couple years ago, we had to integrate contributions from a lot of newcomers which required us to define a set of rules for everyone to follow. Nowadays, those rules are pretty well understood and respected but we are facing new issues. Some of the rules that have helped us create a coherent code base are now getting in our way and some others have not been updated to prevent new kinds of errors.

As a result, we need to change some of our architectural tests in order to make our safety net evolve with our code.