feat(conference.js): add isParticipantConnectionActive

conference.js

@@ -691,6 +691,29 @@ export default {
     isConnectionInterrupted () {
         return connectionIsInterrupted;
     },
+    /**
+     * Finds JitsiParticipant for given id.
+     *
+     * @param {string} id participant's identifier(MUC nickname).
+     *
+     * @returns {JitsiParticipant|null} participant instance for given id or
+     * null if not found.
+     */
+    getParticipantById (id) {
+        return room ? room.getParticipantById(id) : null;
+    },
+    /**
+     * Checks whether the user identified by given id is currently connected.
+     *
+     * @param {string} id participant's identifier(MUC nickname)
+     *
+     * @returns {boolean|null} true if participant's connection is ok or false
+     * if the user is having connectivity issues.
+     */
+    isParticipantConnectionActive (id) {
+        let participant = this.getParticipantById(id);
+        return participant ? participant.isConnectionActive() : null;
+    },
     getMyUserId () {
         return this._room
             && this._room.myUserId();