Bug in Crate affecting blockage migration

Lox's blockage migration protocol has been altered from the original design to account for a bug in the zkp crate that's triggered when a public value is 0 (the identity element of the Ristretto group. This should ideally be fixed so that it doesn't cause other potential issues. Lox currently has the server encrypt the value to get around this bug but it should be revealed to be LEVEL_INVITATIONS for the new trust level.