Add back limit on tag count, raised defaults

In order to prevent unbounded term generation, add back tag count
limit to the query generator.

Updated defaults to reflect the great increase in speed.

app/logical/post_query_builder.rb

@@ -135,6 +135,10 @@ class PostQueryBuilder
       q = Tag.parse_query(query_string)
     end
 
+    if q[:tag_count].to_i > Danbooru.config.tag_query_limit
+      raise ::Post::SearchError.new("You cannot search for more than #{Danbooru.config.tag_query_limit} tags at a time")
+    end
+
     should   = [] # These terms are ORed together
     must     = [] # These terms are ANDed together
     must_not = [] # These terms are NOT ANDed together

app/models/user.rb

@@ -556,13 +556,7 @@ class User < ApplicationRecord
     end
 
     def tag_query_limit
-      if is_platinum?
-        Danbooru.config.base_tag_query_limit * 2
-      elsif is_gold?
-        Danbooru.config.base_tag_query_limit
-      else
-        2
-      end
+      40
     end
 
     def favorite_limit

config/danbooru_default_config.rb

@@ -181,14 +181,14 @@ module Danbooru
 
     # Users cannot search for more than X regular tags at a time.
     def base_tag_query_limit
-      6
+      20
     end
 
     def tag_query_limit
       if CurrentUser.user.present?
         CurrentUser.user.tag_query_limit
       else
-        base_tag_query_limit * 2
+        base_tag_query_limit
       end
     end