IIR Prefilter für WFS in die Funktionen
wfs_iir_prefilter
get_Shelve_Lagrange
Added a progress_bar function
Deleted no longer needed nearest neighbour searches
Integrated new IIR WFS pre filter
Fixed HRTF extrapolation
Added IIR filter to wfs_preequalization()
Added x0 as return value to ir_* functions
Added x0(:,7) to the points ource, line source, etc. wave fields
Fixed conf.X0 to conf.secondary_sources.center
Added function to generate images for README