Refactor NotificationController
Refactor NotificationController

Since there are more methods of following a channel now, we can't just
simply observe the LivestreamerController. Listen for `createRecord`
events fired from the adapter and then check if the channel is online.

bastimeyer/livestreamer-twitch-gui,bastimeyer/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,arclupin/livestreamer-twitch-gui,Klaudit/livestreamer-twitch-gui,Klaudit/livestreamer-twitch-gui,Klaudit/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,arclupin/livestreamer-twitch-gui,chhe/livestreamer-twitch-gui,Rekapper/livestreamer-twitch-gui,bastimeyer/livestreamer-twitch-gui,Rekapper/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,Rekapper/livestreamer-twitch-gui,chhe/livestreamer-twitch-gui,chhe/livestreamer-twitch-gui,arclupin/livestreamer-twitch-gui