Add sanity check for time-steps and exact timing

Description

Add check for incompatible time-step and interaction timing. A test for this feature is also added.

To be able to implement this in a clean and simple way, some refactoring was needed. A bug was found and fixed in the process.

News snippet

Add check for incompatible time-step and interaction timing.

Closes #829 (closed)

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.