Bug 912849 - part1 - WebAPI: notify conference call error. r=khuey, sr=gene.lian
Bug 912849 - part2 - internal API: notifyConferenceError. r=vicamo
Bug 912849 - part3 - IPC & DOM impl. r=khuey
Bug 912849 - part4 - gonk & ril impl. r=vicamo
Bug 912849 - part5 - BT impl. r=gyeh
Bug 912849 - part6 - interface tests. r=khuey