Store list of emails inside user.

    I was thinking that the user->email lookup table would work, but if the
    user is the primary key, then multiple inserts will just overwrite the
    email, not create multiple records. we can make life simpler by just
    putting the list inside the user record anyway.
add function to deserialize lists, returned as raw Buffers by helenus
remove big stale todo
keep cassandra utility functions together
Fill in some more functions & use client.cql