Aded Data Helper and Session Helper

These are two objects I find myself using a lot. I feel like the Class Name "Data" might be a bit too generic and would advise an alternate name, nothing came to mind right away.
same comment as with getVars, i would unpack this:

```php
if ($vars) {
    $_SESSION = array_diff_key($_SESSION, array_flip($vars));
} else {
    $_SESSION = [];
}
```

and no return value necessary.