Fix infinite loops in chat.py

[dufferzafar]

Facebook's thread_info.php now requires a timestamp in the headers. And it must be the same timestamp as the previous thread's last message.

So, please update the chat.py & group_chat.py scripts.

Please refer to these upstream changes:

Fix on RaghavSood's Scraper

Some more discussion

[dufferzafar]

I also feel that the code in those scripts is a bit too terse, so I refactored them a bit here. You might want to have a look.