Refactor and further develop BaseCrawler, rewrite HttpHeadResponse

[peterbencze]

• BaseCrawler

Callback methods do not need to be abstract (template pattern).
The driver should always be closed, even if an exception occurs.
Rename onUrlOpen to onBrowserOpen
Rename onEnd to onFinish

Add new callback: onBrowserTimeout - this method is called when the request times out in the browser.
Add new public method: stop - this method is used to stop the crawler.

• HttpHeadResponse

This class will be used as a parameter in specific callbacks. It should contain the URL of the response and all the non-setter methods that HttpResponse provides.