Heroku integration with foreman

Add foreman configuration for Heroku:
- To test production configuration execute NODE_ENV=production foreman
  start
- Database connection configuration now handles "use_env_variable" which
  should be defined as a environment variable such as "DATABASE_URL"
  with a proper database URI connection string, ie:
  postgres://user:password@db.example.com:5432/database
- Added package.json configuration to run migrations and db seed after
  `npm install`

Update frontend models to match sequelize definition.
Update views to work according to the changes above.
Handling isCompleted and parentId apropiately for PostgreSQL databases

public/javascripts/views/list.js

@@ -37,8 +37,8 @@ TaskView
         model: task
       });
       var a = taskView.render();
-      if (a.model.get('parent_id')!=0)
-        a.$el.insertAfter($('*[data-id="'+a.model.get('parent_id')+'"]').parents('li:first'));
+      if (a.model.get('parentId')!=0)
+        a.$el.insertAfter($('*[data-id="'+a.model.get('parentId')+'"]').parents('li:first'));
       else
         this.$el.append(a.el);
     }