Use custom amOnPage() function in Client

Default Codeception's Universal Connector is trying to fetch
headers() data via headers_list() function. It, however, returns an
empty array since PHP ~v5.1 when executed in CLI environment.
More details here:
https://github.com/Codeception/Codeception/issues/1031

The current solution in OpenMVC Codeception Module is to use PHP XDebug extension's
`xdebug_get_headers()` function which works just fine if your
PHP installation contains XDebug extension.

This allows to track Redirects in functional app.

Here is how a redirect test should be tested.

App code for `/foo` page:

```
header('Location: /bar', true, 303);
header('status: 303');
```

Test:

```
$I->amOnPage('/foo');
$I->seeCurrentUrlEquals('/bar');
```