Auto-promote DanbooruBot to Mod. Auto-create DanbooruBot if it doesn't exist.

test/unit/dmail_test.rb

@@ -177,7 +177,7 @@ class DmailTest < ActiveSupport::TestCase
     context "that is automated" do
       setup do
         @bot = FactoryGirl.create(:user)
-        Danbooru.config.stubs(:system_user).returns(@bot)
+        User.stubs(:system).returns(@bot)
       end
 
       should "only create a copy for the recipient" do

test/unit/post_disapproval_test.rb

@@ -85,7 +85,7 @@ class PostDisapprovalTest < ActiveSupport::TestCase
 
         should "dmail the uploaders" do
           bot = FactoryGirl.create(:user)
-          Danbooru.config.stubs(:system_user).returns(bot)
+          User.stubs(:system).returns(bot)
 
           assert_difference(["@uploaders[0].dmails.count", "@uploaders[1].dmails.count"], 1) do
             PostDisapproval.dmail_messages!

test/unit/post_replacement_test.rb

@@ -20,7 +20,7 @@ class PostReplacementTest < ActiveSupport::TestCase
     Delayed::Worker.delay_jobs = true # don't delete the old images right away
 
     @system = FactoryGirl.create(:user, created_at: 2.weeks.ago)
-    Danbooru.config.stubs(:system_user).returns(@system)
+    User.stubs(:system).returns(@system)
 
     @uploader = FactoryGirl.create(:user, created_at: 2.weeks.ago, can_upload_free: true)
     @replacer = FactoryGirl.create(:user, created_at: 2.weeks.ago, can_approve_posts: true)

test/unit/user_test.rb

@@ -28,7 +28,7 @@ class UserTest < ActiveSupport::TestCase
 
       should "send an automated dmail to the user" do
         bot = FactoryGirl.create(:user)
-        Danbooru.config.stubs(:system_user).returns(bot)
+        User.stubs(:system).returns(bot)
 
         assert_difference("Dmail.count", 1) do
           @user.promote_to!(User::Levels::GOLD)