Added bool for only_rotation. More testing.

Testing (calculation of derivatives, the most used application)
shows some slow down:

80 atoms:0.009975 (old) 0.012618 (new)
160 atoms:0.016126 (old) 0.023345 (new)
320 atoms:0.027697 (old)0.035689 (new)
640 atoms:0.051971 (old) 0.067410 (new)
1280 atoms:0.101560 (old) 0.131484 (new)

(30% slower) which is connected to building up intermediate data for more flexibility