Split up the checking resoruce response and adding the (accepted) event to

Split up the checking resoruce response and adding the (accepted) event to
the resource's calendar.

This is needed because we need the event to have a guid when it's added to
the resource's calendar, otherwise they end up with different GUIDs. This also
gives us some protection against an inconsistent state if there were to be an issue
saving the event to storage after it's been added to the resource's calendar.