make PASS command work for authentication

The previous work on this (https://github.com/flowdock/oulu/pull/31) didn't result in a working implementation. The attached code works for me when testing with LimeChat (a fairly generic IRC client for OS X). 

Comments about the changes:

pass_command.rb:
  - email should be ignored by this command. the RFC specifies 'PASS pass', with no email.

user_command.rb
  - email should be taken directly from the user input