Add the EnvUser with tests. Create an Environment user during bootstrap

Added the EnvUser doc

Support for setting the last login time for the EnvUser

Added a factory for adding the envuser

Admin EnvUser gets added at bootstrap time

Removed a couple of attributes from the upgrade package that no longer needed to be there

EnvironmentUser represents a given user's access to an environment. In each environment, there should be no more than one EnvironmentUser per user.