users: set default settings in ruby instead of in database.

Specify the default settings for new users inside the User model instead
of inside the database. This makes it easier to change defaults, and it
makes the code clearer.

db/migrate/20210115015308_remove_defaults_from_users.rb

@@ -0,0 +1,22 @@
+class RemoveDefaultsFromUsers < ActiveRecord::Migration[6.1]
+  def change
+    change_table(:users) do |t|
+      t.change_default :level, from: 20, to: nil
+      t.change_default :last_logged_in_at, from: "now()", to: nil
+      t.change_default :last_forum_read_at, from: "1960-01-01 00:00:00", to: nil
+      t.change_default :comment_threshold, from: 0, to: nil
+      t.change_default :default_image_size, from: "large", to: nil
+      t.change_default :blacklisted_tags, from: "spoilers\nguro\nscat\nfurry -rating:s", to: nil
+      t.change_default :time_zone, from: "Eastern Time (US & Canada)", to: nil
+      t.change_default :post_update_count, from: 0, to: nil
+      t.change_default :note_update_count, from: 0, to: nil
+      t.change_default :favorite_count, from: 0, to: nil
+      t.change_default :post_upload_count, from: 0, to: nil
+      t.change_default :per_page, from: 20, to: nil
+      t.change_default :bit_prefs, from: 0, to: nil
+      t.change_default :unread_dmail_count, from: 0, to: nil
+      t.change_default :theme, from: 0, to: nil
+      t.change_default :upload_points, from: 1000, to: nil
+    end
+  end
+end