ImportKeys: Add import single key from file

- Refactoring needed

OpenKeychain/src/main/res/layout/import_keys_list_item.xml

@@ -105,6 +105,7 @@
             android:padding="8dp">
 
             <Button
+                android:id="@+id/import_item_button"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
                 android:background="?android:attr/selectableItemBackground"