FIX: When disagreeing with a flag that silenced a user, unsilence them

Previously it would unhide their post but leave them silenced.

This fix also cleans up some of the helper classes to make it easier
to pass extra data to the silencing code (for example, a link to the
post that caused the user to be silenced.)

This patch also refactors the auto_silence specs to avoid using
stubs.

spec/integration/same_ip_spammers_spec.rb

@@ -2,7 +2,7 @@
 
 require 'rails_helper'
 
-describe SpamRulesEnforcer do
+describe "spammers on same IP" do
 
   let(:ip_address)  { '182.189.119.174' }
   let!(:spammer1)   { Fabricate(:user, ip_address: ip_address) }