Save track files in new Sound model:

* Consolidate migrations
* Add Sound model. Each sound can belong to a track and contains
  informations about one sound file.

db/migrate/20110916003929_create_sounds.rb

@@ -0,0 +1,15 @@
+class CreateSounds < ActiveRecord::Migration
+  def up
+    create_table :sounds do |t|
+      t.integer :track_id
+      t.string  :sha256
+      t.string  :mime_type
+
+      t.timestamps
+    end
+  end
+
+  def down
+    drop_table :sounds
+  end
+end