pagination: avoid counting pages outside searches.

Replace this common pattern in controllers:

    @tags = Tag.search(search_params).paginate(params[:page], :limit => params[:limit], :search_count => params[:search])

with this:

    @tags = Tag.paginated_search(params)

`search_count` is used to skip doing a full page count when we're not
doing a search (on the assumption that the number of results will be
high when not constrained by a search). We didn't do this consistently
though. Refactor to do this in every controller.

app/controllers/post_flags_controller.rb

@@ -8,8 +8,7 @@ class PostFlagsController < ApplicationController
   end
 
   def index
-    @post_flags = PostFlag.search(search_params).includes(:creator, post: [:flags, :uploader, :approver])
-    @post_flags = @post_flags.paginate(params[:page], limit: params[:limit])
+    @post_flags = PostFlag.paginated_search(params).includes(:creator, post: [:flags, :uploader, :approver])
     respond_with(@post_flags)
   end