This changes the way the event index is initialized, if it's disabled in
the settings it will not be initialized at all, before only the crawler
loop was not being started.
We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.
The checkpoints don't seem to be loaded anymore in the onSync method,
the reason why this has stopped working is left unexplored since loading
the checkpoints makes most sense during the initialization step anyways.
