Add new status update message type

[Patrik-Stas]

• Message type MSGTYPE_UPDATE_MSG_STATUS_BY_CONNS has following format

{
    "@type": <MSGTYPE_UPDATE_MSG_STATUS_BY_CONNS>,
    "statusCode": "MS-106",
    "uidsByConns": [{"pairwiseDID":"6FRuB95abcmzz1nURoHyWE","uids":["Br4CoNP4TU"]}, ...]
}

• In PR Optimize message status updates #159 we changed behaviour of MSGTYPE_UPDATE_MSG_STATUS_BY_CONNS such that values pairwiseDID are ignored and simply merge of uid is performed, whereas we guarantee on DB level that uids are unique across all agent connections.

We should deprecate MSGTYPE_UPDATE_MSG_STATUS_BY_CONNS and replace it by new message type with simpler argument interface.
Proposal

{
    "@type": <MSGTYPE_UPDATE_MSG_STATUS_BY_UID>,
    "statusCode": "MS-106",
   "uids":["Br4CoNP4TU", ... ] 
}