Do not rethrow errors (prevents reload) and suppress missing Notification API errors

PR for #18

I removed rethrowing all-together, personally I don't see the point of the page reloading automatically on error (since it will just error then anyway...). Feel free to disagree and I'll re-add it (`else if (level !== 'console') {`?).

Also removed an "incorrect" use of `window.setTimeout`, `setTimeout` is a JavaScript feature and not a window/browser feature.

Quick testing shows no issues and it working as intended.