More webrtc backports and fixes

indra/newview/app_settings/settings.xml

indra/newview/app_settings/settings_alchemy.xml

indra/newview/llappviewer.cpp

indra/newview/llavataractions.cpp

indra/newview/llfloaterimsession.cpp

indra/newview/llfloaterimsession.h

indra/newview/llfloaterimsessiontab.cpp

indra/newview/llfloaterimsessiontab.h

indra/newview/llvoicechannel.cpp

indra/newview/llvoiceclient.cpp

indra/newview/llvoiceclient.h

indra/newview/llvoicevivox.cpp

indra/newview/llvoicevivox.h

indra/newview/llvoicewebrtc.cpp

indra/newview/llvoicewebrtc.h

.../newview/skins/default/xui/en/panel_preferences_sound.xml