Source magnetization direction should not be optional in reduction to the pole

[leouieda]

One of my biggest pet peeves in magnetics is people using reduction to the pole indiscriminately in large areas where there is clearly remanent magnetization present. Many don't even realize that this is a problem. My theory is that this is because most software don't ask for the magnetization direction (or even allow you to set one) and implicitly assume induced magnetization only, leading to the impression that reduction to the pole only needs the field direction.

I would argue that we can make this assumption more explicit by making the magnetization inclination and declination required arguments of our functions. Right now, they default to None which ends up meaning "induced magnetization" (this link may or may not be obvious as well). Removing the option will also result in less code since we don't have to check that both inc and dec were given.