Java client BECN implementation (#155)

Java/src/discovery/DiscoveryConnectionCallback.java

@@ -0,0 +1,14 @@
+package gov.nasa.xpc.discovery;
+
+import gov.nasa.xpc.XPlaneConnect;
+
+public interface DiscoveryConnectionCallback {
+
+    /**
+     * Helper callback called when a 1st XPlanePlugin is discovered. When the 1st packet is received, an XPlaneConnect
+     * instance is created and the discovery is stopped.
+     *
+     * @param xpc The XPlaneConnect instance configured with the discovered
+     */
+    void onConnectionEstablished(XPlaneConnect xpc);
+}