Add Reminders table to database

[seesarahcode]

• Create Reminders table
• Add publication_id column - integer
• Add task_id column - integer
• Add draft_id column - integer
• Add recipient_id column - integer
• Add send_date column - datetime
• Add for_author column - boolean
• Add validation for publication_id column (presence)
• In Publications table add: has_many :reminders
• Reminders table should: belongs_to :publication
• In Drafts table should: has_many :reminders
• Reminders table add: belongs_to :draft
• In Tasks table should: has_many :reminders
• Reminders table add: belongs_to :task
• Update Drafts model: when reminder_frequency is updated, delete all Reminders and rebuild team
• Create factories
• Write passing unit tests
• Create seed data