runApp function
Attaches the given app
to the document's body by initializing it.
Implementation
void runApp(final Widget app) {
print(r'''
_____ __ ___ _
| __ \ /\ \ / / \ | |
| | | | / \ \ /\ / /| \| |
| | | |/ /\ \ \/ \/ / | . ` |
| |__| / ____ \ /\ / | |\ |
|_____/_/ \_\/ \/ |_| \_|
''');
_appNode?.dispose();
_appNode = app.createNode()
..parentNode = null
..initialize();
}