Adding a laravel backup artisan command

* Backups can be stored in an s3 Bucket or on disk
Adding AWS package to support backups
Adding config files for s3 backups

* AWS configuration and backup package config

* Refactoring symlink creation
Fixing symlink paths
Adding backup command to capistrano
Merge pull request #378 from DoSomething/backup

Adding a laravel backup artisan command