Make reload atomic

[romaninsh]

Currently jsReload() contains 2 actions - replace content with spinner, then load new content and replace. This PR combines them into a single method call. This way if we pass some expression based on the content that is about to be reloaded, we won't loose it due to spinner.

$grid = $page->add('Grid');
$grid->menu->addItem('Complete Selected', new \atk4\ui\jsReload($grid->table, [
    'delete'=>$grid->addSelection()->jsChecked()
]));
var_dump($_GET);

jsChecked is cleared by spinner and passed as empty string into reloadView.

[DarkSide666]

I am not JS expert, but looks good to me.