search: support quoted values for all metatags.

Support using quoted values with all metatags. For example: user:"blah blah",
pool:"blah blah", commentary:"blah blah", etc. Things like rating:"safe",
id:"42" also work. Both single and double quotes are supported.

Also make the status: and rating: metatags fully free. Before only
status:deleted and rating:s were free.

config/danbooru_default_config.rb

@@ -108,8 +108,8 @@ module Danbooru
     end
 
     # Return true if the given tag shouldn't count against the user's tag search limit.
-    def is_unlimited_tag?(tag)
-      tag.match?(/\A(-?status:deleted|rating:s.*|limit:.+)\z/i)
+    def is_unlimited_tag?(term)
+      term.type == :metatag && term.name.in?(%w[status rating limit])
     end
 
     # After this many pages, the paginator will switch to sequential mode.