Exec rails g model picture

rails g model picture user_id:integer provider:string \
provider_picture_id:integer data:text original_created_at:timestamp \
original_update_at:timestamp

provider_picture_id: bigint
add_index: user_id
add_index: [user_id, provider_picture_id, provider]
Add unique restriction
Add association
Implement Picture::find_or_create_from_response
Mark pending