preprocessing notebook - fixes and updates

[PeerHerholz]

The preprocessing notebook should be revised wrt to multiple things:

• [ ] overall, more information with respect to the workflow should be provided, especially in the beginning and within the single processing steps

• [ ] unused cells and output should be deleted

• [ ] adjust the coregistration by incorporating the WM

• [ ] include a datasink node to adjust output files that are conform with the BIDS derivatives extension (common derivatives, structural derivatives, functional derivatives)

• [ ] include functionality to delete unused working directory output

• [ ] include "checks" at the end of the notebook: visualization of the realignment parameters, all coregistrations, applied mask, detrending

[PeerHerholz]

Once implemented, the PR will be reviewed from @kesslerr and me.