Adds activity tab for system emails

app/controllers/admin/activity_controller.rb

@@ -1,5 +1,5 @@
 class Admin::ActivityController < Admin::BaseController
-  has_filters %w{all on_users on_proposals on_debates on_comments}
+  has_filters %w{all on_users on_proposals on_debates on_comments on_system_emails}
 
   def show
     @activity = Activity.for_render.send(@current_filter)

app/models/activity.rb

@@ -11,6 +11,7 @@ class Activity < ActiveRecord::Base
   scope :on_users, -> { where(actionable_type: 'User') }
   scope :on_comments, -> { where(actionable_type: 'Comment') }
   scope :on_budget_investments, -> { where(actionable_type: 'Budget::Investment') }
+  scope :on_system_emails, -> { where(actionable_type: 'ProposalNotification') }
   scope :for_render, -> { includes(user: [:moderator, :administrator]).includes(:actionable) }
 
   def self.log(user, action, actionable)

app/models/proposal_notification.rb

@@ -10,6 +10,7 @@ class ProposalNotification < ActiveRecord::Base
   validates :proposal, presence: true
   validate :minimum_interval
 
+  scope :with_hidden, -> { all }
   scope :public_for_api,           -> { where(proposal_id: Proposal.public_for_api.pluck(:id)) }
   scope :sort_by_created_at,       -> { reorder(created_at: :desc) }
   scope :sort_by_moderated,       -> { reorder(moderated: :desc) }