Implement Orientation matrix logic for Sequences

Conceptually I was thinking of having a Sequence property mapping/registering blocks to orientation matrices. These matrices could be applied to the registered gradients and corresponding RFpulses right before calling the sequence to grid conversion. Hence, plotting would directly incorporate the rotated gradients and modified frequency modulation.

Applying an orientation matrix could be different from mutating the building block object, such that the application returns the transformed waveform instead of using the 'rotate_gradients' function of the object.

As first step I would suggest implementing an O-matrix class, and tackle the block-registration inside the Sequence after that.