This commit moves the device token logic to a new
PushNotificationClient, to move complexity from this specific feature
away from damusApp.swift
This commit also slightly improves the handling of device tokens, by
caching it on the client struct even if the user is using local
notifications, so that the device token can be sent to the server immediately after
switching to push notifications mode.
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Reviewed-by: William Casarin <jb55@jb55.com>