Review "IP address has changed" functionality

The "IP address has changed" functionality is dodgy. Worse, when allow_reverse_proxy is used, the X-Forwarded-For header is trusted implicitly without validation.

https://github.com/beefproject/beef/blob/943a6fd2266f2652e64885c499e8f8fb5735ac10/core/main/handlers/hookedbrowsers.rb#L93-L102

Here's an example someone provided, showing that the stored IP address contains two IP addresses separated by ,.

It may also result in many "IP address has changed" events in load balanced environments. Although I'm not sure that this is avoidable.