1. subscribe.component: disable subscribe/unsubscribe button when already pushed | add notification when subscribe/unsubscribe fails.2. subscribe.service: return null in 'isSubscribedToCommunity' function if request fails.
1. subscribe.component: disable subscribe/unsubscribe button when already pushed | add notification when subscribe/unsubscribe fails.
2. subscribe.service: return null in 'isSubscribedToCommunity' function if request fails.