Add electromagnetic automated tests

[HanneThienpondt]

I will add the tests when I have time. I added Michael Hardman as an assignee, just so you will get an update when the tests are up and running.

Numerical test to include:

• [ ] Check apar2 time evolution
• [ ] Check bpar2 time evolution

Benchmark tests to include:

• [ ] KBM
• [ ] MTM
• [ ] Alfven Eigenmode