2FA (response 406) and possible login error 405 fixes

[usvi]

This pull request should help in 2 problems:

1. The 2 factor authentication code should now be managed automatically and user instructed how to input it
2. We should now get less, maybe even zero events were Facebook kicks us and notifies us: "User must verify their account on www.facebook.com (405)"

Technically

• Introduced machine_id props and automatic requesting which I speculate helps in the 405 situation.
• 2FA first_factor and the twofactor access code props, storing and use.
• Automatic use of the 2FA when user has set the twofactor access code.
• Twofactor access code automatic invalidation if dependent data has changed or on critical error.
• Prompt about how to set the twofactor code.

[usvi]

Solved the original error by the reporter here: https://github.com/bitlbee/bitlbee-facebook/issues/215