Support "new Facebook" UI

[singpolyma]

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 <module>
    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