Removed no longer needed WFS functions for one point

The same can now achieved by wave_field_mono_wfs()
Added extra function for calculating NFCHOA order

Also added the possibility to give the order N as a parameter to the low level
NFCHOA driving functions
cleaned up comments
Removed automatic setting of conf.plot.usedb=1
fixed a bug
Appending zeros are now handled by conf.N
Fixed a bug regarding varargout handling
Ensure wfs_prefilter returns a row_vector
reverted last commit
Added the new dirac_imp() to the driving functions
Added extra function to find zeros of spherical hankel function
Added dirac_imp() to generate stimulus for imp wave fields
Switched back to real dirac pulse for binaural simulations
Added low level imp driving functions for NFCHOA
Added an extra function for bilinear transform
Updated imp NFCHOA wave fields to new structure