Support "new Facebook" UI

## Description of the problem

When I have switched my web UI to the "new Facebook" UI, then fbchat login no longer works. Switching back to "classic UI" and it works again.

## Traceback
```
Traceback (most recent call last):
File "t.py", line 3, in
session = fbchat.Session.login(REDACTED)
File "/home/singpolyma/src/fbchat/fbchat/_session.py", line 250, in login
return cls._from_session(session=session)
File "/home/singpolyma/src/fbchat/fbchat/_session.py", line 317, in _from_session
raise _exception.NotLoggedIn("Could not find fb_dtsg")
fbchat.NotLoggedIn: Could not find fb_dtsg
```