Soft launch multi-factor authentication

Went off into a bit of a rabbit hole...

Had implemented most of the code for MFA but wanted to soft launch. This led me to looking at how to implement feature flags in a Rails app and the Rollout gem. That then led me to the RolloutUI gem.

After much fiddling, I now have a nice dashboard to manage feature releases and MFA is available to approximately 30% of my users and will increase to 100% by 18 April. Also integrated Headway for product announcements.