Deployment script variables

Hi!

I've been a long time user of similar software to Vito. They had deploy script variables to make deployments on servers with multiple software versions way more efficient.

Example:

```

{RELOAD_PHP_FPM}

cd {SITE_DIRECTORY}

{SITE_PHP} ./console.php assets:build:js

{SITE_PHP} ./console.php assets:build:css

{SITE_PHP} ./console.php assets:build:elfinder

{SITE_PHP} ./doctrine.php orm:clear-cache:metadata

{SITE_PHP} ./doctrine.php orm:clear-cache:query

{SITE_PHP} ./doctrine.php orm:clear-cache:result

{SITE_PHP} ./doctrine.php orm:generate-proxies
```

It'd be awesome to have this in Vito too.