Separating User from UserProperties structs

* For clarity, separating User from UserProperties
Moved UserService initializer into new directory
Service implementation now using exceptions

* ActiveRecord validation and not-found exceptions are caught and re-thrown as Barrister::RpcException
Enforcing uniqueness of email address in users table
Updating error codes:

* 100 means validation error
* 101 means entity not found
Controllers now plumb BarristerRpc::Exception as strings to the views
Removing BarristerRpcResult class and catching exceptions in controller

* Removed the intermediary class, because it didn't cut down on any codes
* Controllers now implement a try/catch for Barrister exceptions
Merge branch 'error_codes'