"-hrtf" command option

The "-hrtf File" decoder command-line option is used for specifying the external HRTF filter File.

I suggest two updates:

1. Print out the existence of an external file if used, similarly as for example for head rotation.

2. Add sanity check to avoid running the decoder with "-hrtf" option in output configurations other than BINAURAL or BINAURAL_OUTPUT.

The same two points apply also to Custom Renderer config. and Custom LS config.

Moreover, the decoder halts when a wrong filename is used. The issue is that the deallocation block is called while the related handles are not initialized.

Finally, there exists a leftover switch FIX_FOR_TEST in decoder.c.