Check to see if there are any active sessions (user logged on) when attempting to change that user's username

There should be a prompt to warn an admin that this user will be logged out if the username is changed.  Currently, if a user is currently logged in, changing their username will break that user's session and result in an error message that states, "No available organizations exist for this user."  The user with the bad login session would have to either wait until their session expires due to inactivity or log out to resolve this issue.