implement stub easy onboarding activity for quicksy

src/quicksy/java/eu/siacs/conversations/ui/EasyOnboardingInviteActivity.java

@@ -0,0 +1,9 @@
+package eu.siacs.conversations.ui;
+
+import eu.siacs.conversations.entities.Account;
+
+public class EasyOnboardingInviteActivity {
+    public static void launch(Account account, XmppActivity activity) {
+        throw new IllegalArgumentException("Easy Onboarding is not implemented for Quicksy");
+    }
+}