Nginx to apache and some fixes

I migrated from Nginx to Apache2 and solved some problems:

* Migrating from MySQL to PostgreSQL on app.json file
* Adding description to env variables on Heroku(to prevent that the user modify it during setup)
* Removing <code>app/config/heroku/</code> folder(all setings are set on <code>.env.heroku.php</code> and this folder is unnecessary)