pagination: refactor page limits.

Refactor page limits to a) be explicitly listed in the User class (not
hidden away in the Danbooru config) and b) explicitly depend on the
CurrentUser (not implicitly by way of Danbooru.config.max_numbered_pages).

test/unit/paginator_test.rb

@@ -3,6 +3,11 @@ require 'test_helper'
 class PaginatorTest < ActiveSupport::TestCase
   setup do
     @posts = FactoryBot.create_list(:post, 5)
+    CurrentUser.user = User.anonymous
+  end
+
+  teardown do
+    CurrentUser.user = nil
   end
 
   context "sequential pagination (before)" do
@@ -37,9 +42,8 @@ class PaginatorTest < ActiveSupport::TestCase
     end
 
     should "raise an error when exceeding the page limit" do
-      Danbooru.config.stubs(:max_numbered_pages).returns(5)
       assert_raises(PaginationExtension::PaginationError) do
-        Post.paginate(10)
+        Post.paginate(10, page_limit: 5)
       end
     end