Adds functions to get and remove local participant property from presence (#783)

JitsiConference.js

@@ -1999,6 +1999,28 @@ JitsiConference.prototype.setLocalParticipantProperty = function(name, value) {
     this.sendCommand(`jitsi_participant_${name}`, { value });
 };
 
+/**
+ *  Removes a property for the local participant and sends the updated presence.
+ */
+JitsiConference.prototype.removeLocalParticipantProperty = function(name) {
+    this.removeCommand(`jitsi_participant_${name}`);
+    this.room.sendPresence();
+};
+
+/**
+ * Gets a local participant property.
+ *
+ * @return value of the local participant property if the tagName exists in the
+ * list of properties, otherwise returns undefined.
+ */
+JitsiConference.prototype.getLocalParticipantProperty = function(name) {
+    const property = this.room.presMap.nodes.find(prop =>
+        prop.tagName === `jitsi_participant_${name}`
+    );
+
+    return property ? property.value : undefined;
+};
+
 /**
  * Sends the given feedback through CallStats if enabled.
  *