[request] remove post fix Request, introduce Reply idea, should replace InteractiveRequest

* Remove postfix `Request` for example CaptureRequest would become just `Capture`.
* Move all so called interactive requests to `Reply` namespace. Now its reply not interactive request.

How it was:

```php
<?php

use Payum\Core\Request\CaptureRequest;
use Payum\Core\Request\SimpleStatusRequest;
use Payum\Core\Request\Http\RedirectUrlInteractiveRequest;

if ($interactiveRequest = $payment->execute(new CaptureRequest($model), true)) {
     if ($interactiveRequest instanceof RedirectUrlInteractiveRequest) {
         header("Location: ".$interactiveRequest->getUrl());
          die();
      }

    throw new \LogicException('Unsupported interactive request', null, $interactiveRequest);
}

$payment->execute($status =  new SimpleStatusRequest($model));

echo $status->getStatus();
```

This is an example of how it will look like:
```php
<?php

use Payum\Core\Request\Capture;
use Payum\Core\Request\GetHumanStatus;
use Payum\Core\Reply\HttpRedirect;

if ($reply = $payment->execute(new Capture($model), true)) {
     if ($reply instanceof HttpRedirect) {
         header("Location: ".$reply->getUrl());
          die();
      }

    throw new \LogicException('Unsupported reply', null, $reply);
}

$payment->execute($status =  new GetHumanStatus($model));

echo $status->getStatus();
```

Feedback is very welcome.