* Refactor to move upgrade logic from UserPromotion to UserUpgrade.
* Send the recipient and the purchaser of a gifted upgrade separate
dmail notifications.
New rules for user promotions:
* Moderators can no longer promote other users to moderator level. Only
Admins can promote users to Mod level. Mods can only promote up to Builder level.
* Admins can no longer promote other users to Admin level. Only Owners
can promote users to Admin. Admins can only promote up to Mod level.
* Admins can no longer demote themselves or other admins.
These rules are being changed to account for the new Owner user level.
Also change it so that when a user upgrades their account, the promotion
is done by DanbooruBot. This means that the inviter and the mod action
will show DanbooruBot as the promoter instead of the user themselves.
This was a hack to deal with the Cloudflare check sometimes being slow
or timing out during tests. The call to https://api.cloudflare.com/client/v4/ips
could hang if there were IPv6 connectivity problems. If this happens, make
sure that IPv6 is configured properly and that `curl -v --http1.1 -6 https://api.cloudflare.com/client/v4/ips`
works.
Create the DanbooruBot account in db/seeds.rb instead of in an
initializer. Move the old db/seeds.rb to db/populate.rb.
Fixes a bug introduced in e2eb45a. Creating DanbooruBot in an
initializer was wrong because in a fresh install the users table doesn't
exist yet. This caused `rake db:migrate` to fail.
