Inform user if signature check fails

OpenPGP-Keychain/res/layout/api_app_error_message.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="fill_parent"
+    android:layout_height="fill_parent"
+    android:orientation="vertical" >
+
+    <org.sufficientlysecure.htmltextview.HtmlTextView
+        android:id="@+id/api_app_error_message_text"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:padding="8dp"
+        android:paddingBottom="0dip"
+        android:text="Set in-code!"
+        android:textAppearance="?android:attr/textAppearanceLarge" />
+
+</LinearLayout>