Allow export of contact keys without encryption

OpenKeychain/src/main/res/menu/export_public.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <item
+        android:id="@+id/menu_export_file"
+        android:title="To file"
+        />
+    <item
+        android:id="@+id/menu_export_share"
+        android:title="Share"
+        />
+</menu>