Add Notifier Access To GroupingHash

[joeblau]

There doesn't seem to be a way to set the groupingHash on iOS.

[jessicard]

Thanks for creating an issue about this @joeblau! We would definitely like to add this to the notifier. We do have plans to add it eventually, but currently we have no ETA. In the meantime, of course, we're open to PRs.

[joeblau]

@jessicard Yep, I'm going to fix this and the breadcrumbs over this weekend. Just had to get approval to do it.