Add activities

[Kitkatnik]

Must Have:

• Manual activities (call, email, in-person appointment)
  • Completed in the past
  • Upcoming / scheduled
• Automatic activities (status change, benefit info change, completed (with outcome of approved, declined, or dropped), re-opened, etc.

Activities have:

• activity_type (enum?)
• notes (optional)
• date (might be different from created_at)
• is_upcoming boolean
• system_generated boolean

Activities list:

• call
• email
• in-person
• form
• mail
• fax
• status changed (system generated)
• re-opened (system generated - but might do this one later)
• benefit changed (system generated - but I might add this in later if it gets too complex)
• other