ext/ffmpeg/: Added helper object to handle extra properties.

ext/ffmpeg/: Added helper object to handle extra properties.

Original commit message from CVS:
Patch by: Mark Nauwelaerts <manauw at skynet dot be>
* ext/ffmpeg/Makefile.am:
* ext/ffmpeg/gstffmpegcfg.c: (gst_ffmpeg_pass_get_type),
(gst_ffmpeg_lim_pass_get_type), (gst_ffmpeg_mb_decision_get_type),
(gst_ffmpeg_mb_cmp_get_type), (gst_ffmpeg_dct_algo_get_type),
(gst_ffmpeg_idct_algo_get_type), (gst_ffmpeg_quant_type_get_type),
(gst_ffmpeg_pre_me_get_type), (gst_ffmpeg_pred_method_get_type),
(gst_ffmpeg_flags_get_type), (gst_ffmpeg_cfg_init),
(gst_ffmpeg_cfg_codec_has_pspec),
(gst_ffmpeg_cfg_install_property), (gst_ffmpeg_cfg_set_property),
(gst_ffmpeg_cfg_get_property), (gst_ffmpeg_cfg_set_defaults),
(gst_ffmpeg_cfg_fill_context):
* ext/ffmpeg/gstffmpegcfg.h:
Added helper object to handle extra properties.
* ext/ffmpeg/gstffmpegenc.c: (gst_ffmpegenc_class_init),
(gst_ffmpegenc_init), (gst_ffmpegenc_dispose),
(gst_ffmpegenc_getcaps), (gst_ffmpegenc_setcaps),
(gst_ffmpegenc_chain_video), (gst_ffmpegenc_chain_audio),
(gst_ffmpegenc_flush_buffers), (gst_ffmpegenc_event_video),
(gst_ffmpegenc_set_property), (gst_ffmpegenc_get_property),
(gst_ffmpegenc_change_state), (gst_ffmpegenc_register):
* ext/ffmpeg/gstffmpegenc.h:
Exposes (quite some of) the AVCodecContext configurable
settings, as well as some additional (though simple) logic for b-frame
delay handling.
Most of the properties are only enabled for mpeg4-like codecs.
Fixes #344583.