DolphinQt/Android: Add warning when converting NKit files

Yes, that's right! It's time to add even more NKit warnings,
because users still don't understand what NKit is or how it works!

More specifically, some users seem to be under the impression that
converting an NKit file to for instance RVZ using Dolphin's convert
feature will result in a normal RVZ file, when it in fact results in
an NKit RVZ file (since NKit is not a container format in the sense
that GCZ/WIA/RVZ/WBFS/CISO is, but rather a kind of trimmed ISO).
I can hardly blame users for not knowing this, because it's not
intuitive unless you know the technical details of how NKit works.

Source/Android/jni/GameList/GameFile.cpp

@@ -162,6 +162,12 @@ JNIEXPORT jboolean JNICALL Java_org_dolphinemu_dolphinemu_model_GameFile_isDatel
   return static_cast<jboolean>(GetRef(env, obj)->IsDatelDisc());
 }
 
+JNIEXPORT jboolean JNICALL Java_org_dolphinemu_dolphinemu_model_GameFile_isNKit(JNIEnv* env,
+                                                                                jobject obj)
+{
+  return static_cast<jboolean>(GetRef(env, obj)->IsNKit());
+}
+
 JNIEXPORT jintArray JNICALL Java_org_dolphinemu_dolphinemu_model_GameFile_getBanner(JNIEnv* env,
                                                                                     jobject obj)
 {