FEATURE: track statistics around post creation

- how long were people typing?
- how long was composer open?
- how many drafts were created?
- correct, draft saved to go away after you continue typing

store in Post.find(xyz).post_stat

db/migrate/20150802233112_add_post_stats.rb

@@ -0,0 +1,16 @@
+class AddPostStats < ActiveRecord::Migration
+  def change
+
+    add_column :drafts, :revisions, :int, null: false, default: 1
+
+    create_table :post_stats do |t|
+      t.integer :post_id
+      t.integer :drafts_saved
+      t.integer :typing_duration_msecs
+      t.integer :composer_open_duration_msecs
+      t.timestamps
+    end
+
+    add_index :post_stats, [:post_id]
+  end
+end