2FA

1) add "Account confirmation" setting with the following values: disabled, by email, by phone, by email and phone (now user is confirmed only when email is confirmed) into Settings > Account
2) add "Enable 2FA" into Settings > Account
3) add new setting category for Twilio with all necessary settings for Twilio (possibly other providers as well - make ability to integrate other providers via 3rd-party modules)
4) when 2FA enabled, after successful login display page with SMS/voice/etc sending page where user can enter the code
5) add phone number field to join form
6) add phone_confirmed field to sys_accounts table
7) display phone verification informer, similar to how email verification informer displayed
8) display email verification informer only when "Account is confirmed when" = "email is confirmed" or "email and phone are confirmed"
9) display phone verification informer only when "Account is confirmed when" = "phone is confirmed" or "email and phone are confirmed"
10) when phone is changed, change phone_confirmed accordingly and repeat verification procedure
11) add possibility to restore password by phone on forgot password page

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