Put back default strings on dialogs

But make them work by calling _t in render rather than
getDefaultProps().

Also sort out some 'Warning!' strings

src/SlashCommands.js

@@ -71,7 +71,6 @@ const commands = {
         Modal.createDialog(ErrorDialog, {
             title: _t('/ddg is not a command'),
             description: _t('To use it, just wait for autocomplete results to load and tab through them') + '.',
-			button: _t("OK"),
         });
         return success();
     }),