Implements #150

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

db/migrate/20180615102215_create_administrator_tasks.rb

@@ -0,0 +1,11 @@
+class CreateAdministratorTasks < ActiveRecord::Migration
+  def change
+    create_table :administrator_tasks do |t|
+      t.references :source, polymorphic: true, index: true
+      t.references :user, index: true, foreign_key: true
+      t.datetime :executed_at
+
+      t.timestamps null: false
+    end
+  end
+end