Add config options to disable comments and the forum.

Add options to disable comments, the forum, and autocomplete. This is
for personal boorus and potentially for safe mode. Note that disabling
the forum may cause difficulties with creating and approving BURs.

Disabling comments and the forum merely hides them from most areas,
rather than completely removing them.

app/logical/autocomplete_service.rb

@@ -28,23 +28,27 @@ class AutocompleteService
 
   TAG_PREFIXES = TagCategory.mapping.keys.map { |prefix| prefix + ":" }
 
-  attr_reader :query, :type, :limit, :current_user
+  attr_reader :query, :type, :limit, :current_user, :enabled
+  alias_method :enabled?, :enabled
 
   # Perform completion for the given search type and query.
   # @param query [String] the string being completed
   # @param type [String] the type of completion being performed
   # @param current_user [User] the user we're performing completion for
   # @param limit [Integer] the max number of results to return
-  def initialize(query, type, current_user: User.anonymous, limit: 10)
+  def initialize(query, type, current_user: User.anonymous, limit: 10, enabled: Danbooru.config.autocomplete_enabled?.to_s.truthy?)
     @query = query.to_s
     @type = type.to_s.to_sym
     @current_user = current_user
     @limit = limit
+    @enabled = enabled
   end
 
   # Return the results of the completion.
   # @return [Array<Hash>] the autocomplete results
   def autocomplete_results
+    return [] if !enabled?
+
     case type
     when :tag_query
       autocomplete_tag_query

app/logical/rate_limiter.rb

@@ -16,7 +16,7 @@ class RateLimiter
   attr_reader :action, :keys, :cost, :rate, :burst, :enabled
   alias_method :enabled?, :enabled
 
-  def initialize(action, keys = ["*"], cost: 1, rate: 1, burst: 1, enabled: Danbooru.config.rate_limits_enabled?)
+  def initialize(action, keys = ["*"], cost: 1, rate: 1, burst: 1, enabled: Danbooru.config.rate_limits_enabled?.to_s.truthy?)
     @action = action
     @keys = keys
     @cost = cost