#47 realtime LADSPA support

[jelmer]

The effect of a particular LADSPA plugin can now only
be listened to after applying the plugin effect after
pressing 'ok'. This makes editing of samples a
laborious job since (at least for me) applying effects
in sweep is a iterative procedure. I think making the
LADSPA plugins work realtime on the selected waveform
should not be a very big and difficult job to do. I
really hope this can work in the near future since for
the rest I absolutely like sweep.