Strict Standards: Non-static method JSite::getMenu() should not be called statically

It's quite simple. Your template calls a function named getMenu() statically. Meaning the call looks like this: $app::getMenu(). But it should look like this: $app->getMenu(). The variable name ($app) doesn't matter, the colon vs arrow matters.

The correct way to get the menu is:

$app = JFactory::getApplication();
$menu = $app->getMenu();

or even shorter:

$menu = JFactory::getApplication()->getMenu();