Include some form of identifier in replayed messages json

Something like:

Old

{
  "type":"talker_join",
  "data":{
    "unixtime":1557219295,
    "quiet":false,
    "user":"imranh",
    "method":"normal",
    "channel":100
  }
}

New

{
  "type":"talker_join",
  "data":{
    "unixtime":1557219295,
    "quiet":false,
    "user":"imranh",
    "method":"normal",
    "channel":100
  },
  "replay": true
}