ios: improved significantly rendering performance

app/ios/RTABMapApp/ViewController.swift

@@ -2337,6 +2337,14 @@ extension Date {
         dateformat.dateFormat = format
         return dateformat.string(from: self)
     }
+    
+    var millisecondsSince1970:Int64 {
+        Int64((self.timeIntervalSince1970 * 1000.0).rounded())
+    }
+    
+    init(milliseconds:Int64) {
+        self = Date(timeIntervalSince1970: TimeInterval(milliseconds) / 1000)
+    }
 }
 
 extension DispatchQueue {