Update reverbation integration code
- Added a getter to the reference of the time on the wavefront
- Modified eigenverb_mono/bi code to use this new time reference
- Added code to generate the width_de/az for spreading ray using the
harmonic mean of distances between the points to the 'left' and 'right'
of the point of the wavefront that collided with the bottom.
- Added default of reverberation_model within the reflection_model
to NULL. Need to add a setter within either wave_queue or
reflection model that allows the user to set the reverberation_model.