Expose track.conference field in types

Local and remote Jitsi tracks expose a reference to the
`JitsiConference` through `track.conference`. This was not available in
the TypeScript definitions.

Local tracks are initialized with `conference = null` but will be set
later, assuming the caller adds the track to a conference. Remote tracks
are always associated with a conference.

types/hand-crafted/modules/RTC/JitsiRemoteTrack.d.ts

@@ -4,6 +4,7 @@ import JitsiConference from '../../JitsiConference';
 
 export default class JitsiRemoteTrack extends JitsiTrack {
   constructor(rtc: RTC, conference: JitsiConference, ownerEndpointId: string, stream: MediaStream, track: MediaStreamTrack, mediaType: any, videoType: any, ssrc: number, muted: boolean, isP2P: boolean);
+  readonly conference: JitsiConference;
   setMute: ( value: boolean ) => void;
   isMuted: () => boolean;
   getParticipantId: () => string;

types/hand-crafted/modules/RTC/JitsiTrack.d.ts

@@ -6,6 +6,7 @@ import TraceablePeerConnection from './TraceablePeerConnection';
 
 export default class JitsiTrack extends EventEmitter {
   constructor( conference: JitsiConference, stream: unknown, track: unknown, streamInactiveHandler: unknown, trackMediaType: MediaType, videoType: VideoType ); // TODO:
+  readonly conference: null | JitsiConference;
   disposed: boolean;
   getVideoType: () => VideoType;
   getType: () => MediaType;