Implement 2-step auth

[marado]

[dissidente]

Currently looking into Speakeasy (https://www.npmjs.com/package/speakeasy) as a 2FA candidate.

Independently of the module to use, I propose the following changes:

• User DB new fields:

2fa_secretKey = 20 char key (given there is no graphic method to relay the secret key it will have to be shown to the user, so it can't be huge otherwise it will be a deterrent of use
2fa_backupKey = one time backup code generated during enrollment to bypass 2FA if OTP device is lost; if prefixed by a given symbol it is considered burned and it will have to be generated again
2fa_status = boolean indicating if 2fa is active for user

• Internal Functions:

2faEnroll - Will take care of user enrollment; generate secretKey and backupKey, validate setup and enable 2fa for user
2faGenerateSecretKey - Generates secret keys and backup codes
2faValidateOTP - Validates provided OTP codes (for enrollment, login, suicide, and other relevant commands (maybe a new command attribute signaling if 2FA is required to 2FA-enabled users?)

• Commands:

[User] 2fa <enable|disable|newbackupcode|status>
[Wizzes] 2faadmin <resetuser|burnbackupcode|status>

[dissidente]

Implemented in #105