enable s3.fog options and install fog by default

i added s3.fog options so you can for example use a different s3 like host with the following options

```
store_with({"engine" => "S3", "settings" => { "s3.access_key_id" => "S3_ACCESS_KEY", "s3.secret_access_key" => "S3_SECRET_ACCESS_KEY", "s3.bucket" => "BUCKET", "s3.path" => "DIR", "s3.keep" => 5, "s3.fog_options" => {  :host => 's3.DUMMY.DOMAIN.COM', :scheme => 'http', :port => 80 } } } )
  action :backup
```

also added fog and build-essentials because it is needed anyway