Implements #150

Adds an entry inside moderation section that allows moderators to check
pending tasks and mark them as solved.

app/models/proposal_executed_dashboard_action.rb

@@ -4,7 +4,14 @@ class ProposalExecutedDashboardAction < ActiveRecord::Base
   belongs_to :proposal
   belongs_to :proposal_dashboard_action
 
+  has_many :administrator_tasks, as: :source, dependent: :destroy
+
   validates :proposal, presence: true, uniqueness: { scope: :proposal_dashboard_action }
   validates :proposal_dashboard_action, presence: true
   validates :executed_at, presence: true
+  validates :comments, presence: true, allow_blank: false, if: :comments_required?
+
+  def comments_required?
+    proposal_dashboard_action&.request_to_administrators? || false
+  end
 end