Notify user on 2FA activation

[Stormix]

Email example:

Hello,

Two-factor Authentication is now active on your account and is required to log in. If you did not request this, or believe it to be in error, please contact support.

Should you have any further questions or comments, please feel free to contact us at the e-mail address listed below.

[issue-label-bot[bot]]

Issue-Label Bot is automatically applying the label feature_request to this issue, with a confidence of 0.62. Please mark this comment with :thumbsup: or :thumbsdown: to give our bot feedback!

Links: app homepage, dashboard and code for this bot.