New EnvUser

Add:
 - the EnvUser doc
 - support for setting the last login time for the EnvUser
 - factory methods for adding the envuser

Create the Admin EnvUser at bootstrap time.
I think that if the CreatedBy isn't specified, we should create a new User, and then use them as the creator.

In the same way that we should create a User for the params.User in order for the name to be used in the environment user.