Add tests for presence of restrore functions within app scripts

src/freedombone-tests

 	FILES=/usr/share/${PROJECT_NAME}/apps/${PROJECT_NAME}-app-*
 
 	# check that these functions exist
-	interface_functions=( install remove backup_local backup_remote upgrade )
+	interface_functions=( install remove backup_local backup_remote restore_local restore_remote upgrade )
 
 	# for all the app scripts
 	for filename in $FILES