the controller initiates a request to a top level page (eg:
album.html.php) which is then free to include whatever other page
chunks it wants with calls like <?= $theme->display('header.html') ?>
Variables like $item and $children are in the global space for all
views.
theme.php helper is now Theme.php library which lets us store the name
of the theme inside the variable itself. This means that the theme
does not have to know its own name because you can use $theme->url()
for all urls to stuff inside the theme itself, which makes it possible
to cline a theme without changing a single line.
Still using the mock album UI.
