gst/wavenc/gstwavenc.*: Set caps on first outgoing buffer, so that it doesn't error out immediately with a non-negoti...

Original commit message from CVS:
* gst/wavenc/gstwavenc.c: (gst_wavenc_base_init),
(gst_wavenc_class_init), (gst_wavenc_init),
(gst_wavenc_create_header_buf), (gst_wavenc_push_header),
(gst_wavenc_sink_setcaps), (get_id_from_name), (gst_wavenc_event),
(gst_wavenc_chain), (gst_wavenc_change_state):
* gst/wavenc/gstwavenc.h:
Set caps on first outgoing buffer, so that it doesn't error out
immediately with a non-negotiated error (#338716). Rewrite and
clean up a bit; fix setcaps function to parse things properly;
fix sink caps (8bit audio is unsigned and doesn't have depth);
use boilerplate macros; remove unused properties stuff.