Bundle all external assets (/wo twemoji)

[mvorisek]

replace & repush of #1782, no twemoji icons (reduce repo size by about 3500 files / 25 MB)

other resources are carefully selected (like we do not need to bundle other fonts than WOFF2)

fixes #1025

external Google Fonts will be bundled in a separate PR (#1784)

temporary, App::cdn paths must be adjusted! - public URL discovery will be added in a separate PR

example temporary fix of your app to be put to the code where you create/init your App instance:

foreach ($app->cdn as $k => $v) {
    $app->cdn[$k] = '/xxx/vendor/atk4/ui' . $v;
}