Bot nameplates (#7391)

* Store actor type in database

* Add bot nameplate to web UI, add setting to preferences, API, AP
Fix #7365

* Fix code style issues

config/locales/en.yml

@@ -49,6 +49,7 @@ en:
     reserved_username: The username is reserved
     roles:
       admin: Admin
+      bot: Bot
       moderator: Mod
     unfollow: Unfollow
   admin:

config/locales/simple_form.en.yml

@@ -4,6 +4,7 @@ en:
     hints:
       defaults:
         avatar: PNG, GIF or JPG. At most 2MB. Will be downscaled to 400x400px
+        bot: Warns people that the account does not represent a person
         digest: Only sent after a long period of inactivity and only if you have received any personal messages in your absence
         display_name:
           one: <span class="name-counter">1</span> character left
@@ -29,6 +30,7 @@ en:
           value: Content
       defaults:
         avatar: Avatar
+        bot: This is a bot account
         confirm_new_password: Confirm new password
         confirm_password: Confirm password
         current_password: Current password