Password reset

1) add PasswordResetController
2) add views for PasswordResetController
3) add specs for PasswordResetController
4) add code for PasswordResetController
5) add validation on password length

Please approve.
btw I just tried it in rails console and find_by_xxxl is undefined method now,
irb(main):001:0> user = User.first
irb(main):002:0> user.find_by_email("tom@example.com")
NoMethodError: undefined method `find_by_email'
Rails core team decided to drop it because of performance issues I think.