Major PBX revamps (including labels, update examples)

cdr.c

channel.c

channels/chan_agent.c

channels/chan_alsa.c

channels/chan_h323.c

channels/chan_iax2.c

channels/chan_local.c

channels/chan_mgcp.c

channels/chan_modem.c

channels/chan_nbs.c

channels/chan_oss.c

channels/chan_phone.c

channels/chan_sip.c

channels/chan_skinny.c

channels/chan_vpb.c

channels/chan_zap.c

configs/extensions.conf.sample

include/asterisk/cdr.h

include/asterisk/channel.h

include/asterisk/pbx.h