Update to Wordpress 3.7.1 + Plugin and config changes

1) added plugin WPRO as git submodule (also fixes a bug with jpeg thumbnails and Amazon S3)
  Easy update with git submodule update, when original repo (git://github.com/alfreddatakillen/wpro.git) changes

2) added plugins disable-wordpress-*-updates
  You need to activate this in plugins. This simply hides all core and plugin update messages, as you cannot update heroku directly anyway. This is to make it easier for non DevOps to use the wordpress install

3) Updated Wordpress base install to current version (3.7.1) and tagged it

4) changed wp-config-sample
AUTOMATIC_UPDATER_DISABLED (New Feature in 3.7.* is disabled - doesn't work on heroku)
DISABLE_WP_CRON to speed up requests. Best to call wp-cron.php manually from another host or through heroku scheduler
Added back logic for local dev environment (DATABASE_URL). Works on heroku and when you work locally auto-changes the URL to the correct one