rate limits: adjust limits for various actions.

* Tie rate limits to both the user's ID and their IP address.

* Make each endpoint have separate rate limits. This means that, for
  example, your post edit rate limit is separate from your post vote
  rate limit. Before all write actions had a shared rate limit.

* Make all write endpoints have rate limits. Before some endpoints, such
  as voting, favoriting, commenting, or forum posting, weren't subject
  to rate limits.

* Add stricter rate limits for some endpoints:

** 1 per 5 minutes for creating new accounts.
** 1 per minute for login attempts, changing your email address, or
   for creating mod reports.
** 1 per minute for sending dmails, creating comments, creating forum
   posts, or creating forum topics.
** 1 per second for voting, favoriting, or disapproving posts.
** These rate limits all have burst factors high enough that they
   shouldn't affect normal, non-automated users.

* Raise the default write rate limit for Gold users from 2 per second to
  4 per second, for all other actions not listed above.

* Raise the default burst factor to 200 for all other actions not listed
  above. Before it was 10 for Members, 30 for Gold, and 60 for Platinum.

app/models/user.rb

@@ -464,26 +464,12 @@ class User < ApplicationRecord
 
       # regen this amount per second
       def api_regen_multiplier(level)
-        if level >= User::Levels::PLATINUM
+        if level >= User::Levels::GOLD
           4
-        elsif level == User::Levels::GOLD
-          2
         else
           1
         end
       end
-
-      # can make this many api calls at once before being bound by
-      # api_regen_multiplier refilling your pool
-      def api_burst_limit(level)
-        if level >= User::Levels::PLATINUM
-          60
-        elsif level == User::Levels::GOLD
-          30
-        else
-          10
-        end
-      end
     end
 
     def max_saved_searches
@@ -534,10 +520,6 @@ class User < ApplicationRecord
       User.api_regen_multiplier(level)
     end
 
-    def api_burst_limit
-      User.api_burst_limit(level)
-    end
-
     def statement_timeout
       User.statement_timeout(level)
     end