Allow user to import/export cards to/from CSV on external storage

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Dutch translations provided by PanderMusubi

app/src/test/java/protect/card_locker/MainActivityTest.java

@@ -50,9 +50,10 @@ public class MainActivityTest
         assertTrue(menu != null);
 
         // The settings and add button should be present
-        assertEquals(menu.size(), 1);
+        assertEquals(menu.size(), 2);
 
         assertEquals("Add", menu.findItem(R.id.action_add).getTitle().toString());
+        assertEquals("Import/Export", menu.findItem(R.id.action_import_export).getTitle().toString());
     }
 
     @Test