gst/audiofx/audiopanorama.*: Add 'method' property and provide a simple (non-psychoacustic) processing method (#394859).

Original commit message from CVS:
Patch by: Sebastian Dröge <slomo circular-chaos org>
* gst/audiofx/audiopanorama.c:
(gst_audio_panorama_method_get_type),
(gst_audio_panorama_class_init), (gst_audio_panorama_init),
(gst_audio_panorama_set_process_function),
(gst_audio_panorama_set_property),
(gst_audio_panorama_get_property), (gst_audio_panorama_set_caps),
(gst_audio_panorama_transform_m2s_int_simple),
(gst_audio_panorama_transform_s2s_int_simple),
(gst_audio_panorama_transform_m2s_float_simple),
(gst_audio_panorama_transform_s2s_float_simple):
* gst/audiofx/audiopanorama.h:
Add 'method' property and provide a simple (non-psychoacustic)
processing method (#394859).
* tests/check/elements/audiopanorama.c: (GST_START_TEST),
(panorama_suite):
Tests for new method.