Push Notification UX Enhancements

After feedback from users of the extension version of web push notifications, one UX issue they've pointed out is that this feature is buried in the UCP, so many users won't know it's available.

In the extension we tried to solve this with adding the Subscribe button to the Notification dropdown as a toggle switch that is available anywhere in the forum and in a place users are likely to check more often than the UCP settings page.

But since subscribing alone is not enough, we also make all web push notifications enabled by default, instead of disabled. That way if a user subscribes, they are done. They only have to visit the UCP settings to tweak the push notifications they are receiving.

Both of these can also be configs in the ACP so the Admin can decide how they want their push notification system to work.