Email verification for multi-node

[bennyschmidt]

For massive multi-node support at the application level, we should allow a fallback option for email/ip verification for protected user actions like new posts.

Example: Sharing content from one Reverse instance to others on different domains that don't share db creds.

In those situations, without access to the Mongo session where the user logged in, the instance would fallback to Dereva's email/ip auth and send a verification before allowing the cross-domain action.