Add who selected, configurable reminders to select, and allow non-OP to select

[dsevillamartin]

Made for Flarum beta 9. Will NOT work in current beta 8.

Changes

• When showing the best answer show who marked it as that answer
• Based on admin configurable permission allow users to mark an answer instead of OP
• Reminder after configurable days to the OP that no answer was marked
  • Uses flagrow/console
  • Adds command wiwatsrt-best-answer:notify
  • Notification is deleted once the user selects a best answer
  • Only notifies if Discussion has at least 1 comment, no best answer chosen, AND hasn't been notified to author yet

Migrations

• Add new columns to discussions table
  • best_answer_user_id — user that selected answer
  • best_answer_notified — if discussion author was notified to select a best answer
  • All existing discussions are set to true to avoid notifying authors of really old discussions