slate example: Disable 'scroll zoom' for WebAssembly

The slate example on https://www.qt.io/web-assembly-example-slate by default has 'scroll zoom' in place. This does not integrate well with the default scrolling on the website, with the result that scroll events seem to be delivered both to the website and the canvas, leading to weird results.

A quick fix for this would be to disable scroll zoom by default in this example.