Observer::notify('user_after_XXX') change

All three notifiers shouldn't use $user->name as passed variable, 
since $user->name cannot uniquely identify user. ($user->username does)

More meaningful variable passed to observer would be $user->id - which 
can uniquely identify user's record in DB.

Added second parameter $user->id and leaved $user->name for backwards compatibility.
Merge pull request #490 from marekmurawski/patch-1

Observer::notify('user_after_XXX') change