reworked keyserver preferences with recyclerview

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

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto">
+
+    <item
+        android:id="@+id/menu_add_keyserver"
+        android:title="@string/menu_search"
+        android:icon="@drawable/ic_add_white_24dp"
+        app:showAsAction="always" />
+</menu>