BSSFP: Returned list of sequence per TR without time-shift to facilitate the use of Sequence concatenation

Currently inside the parametric definition of a bSSFP the sequence blocks per TR are shifted such that when using the Addition (add/+) logic of sequences and blocks the result is correct. I would argue that this shift should not be done explicitly but by using the Sequence.concatenate logic.

Code proposal

    # When to start with ro blocks
    seq_list = []
    for tr_idx, ro_b in enumerate(ro_blocks):
        ro_b.shift_in_time(rf_block.duration - ss_refdur)
        seq = compensated_rf + ro_b
        seq_list.append(seq)
    return seq_list