Dipoles in Opal-T to support quadrupole component field gradients
The following discussion from !269 (merged) should be addressed:
The commenting out was introduced by @kraus in 595b4b83 .. perhaps he can comment. Note that the class at that time was called
@kraus The dipoles in Opal-T used to support field gradients in version 1.6 and before. When I rewrote Opal-T I disabled it to speed up the development. However it was my intention to re-enable it (but didn't happen). I still think that we should support the quadruple component.