Implement simple notifications on backend

[ed-software]

• [x] Add a new table Notifications to the database
  • Notification type: Enum (RecipeLiked, RecipeCommented, CommentLiked, CommentReplied)
  • Created at: Time
  • Read: Boolean
  • For: User
  • Concerns: User
• [x] Update table on:
  • [x] Recipe liked
  • [x] Recipe commented on
  • [x] Comment liked
  • [x] Comment replied to
• [x] Add Notifications query
• [x] Add ReadNotifications mutation
• [x] Order notifications in chronological order
• [x] Add pagination to notifications
• [x] Add NotificationCount query
• [x] Add linkId to table