Cleaned up input parameters for nonco bfields.

Remove some inputs that were moved to atom-wise switches in
nonco_angle.dat and some for functionality that was not implemented.

Changed the rest to form a more consistent interface.
Keeping a switch to turn everything off. If that switch is turned on,
this implies calculating the torque and constraint magnetism in general.
The fields are calculated for all atoms where that is specified in
the nonco_angle.dat.
It does not anymore imply external fields: There is a new switch for that.
If that is turned on, a file with external fields must be provided.
Introduced a verbosity parameter for bfields, select between no output,
summary and detailed information.

See comments and documentation for details.

Changed output depending on the new input parameter.