add TrackedProperty

This will be used for updating inventory slots when ItemStack properties change

server/TrackedProperty.ts

@@ -0,0 +1,23 @@
+export class TrackedProperty<T> {
+	private trackedValue?:T;
+	private updateCallback?:(value:T) => void;
+
+	constructor(initialValue?:T) {
+		this.trackedValue = initialValue;
+	}
+
+	public set OnChange(value:() => void) {
+		this.updateCallback = value;
+	}
+
+	public get Value() {
+		return this.trackedValue;
+	}
+
+	public set Value(value) {
+		this.trackedValue = value;
+		if (this.updateCallback && value) {
+			this.updateCallback(value);
+		}
+	}
+}