when one user logged in in different browsers, kill user's previous session automatically.
In order to implement this, add a property to make this feature configurable.
1) one user logged in LR web site in one browser, getting session I;
2) one user logged in LR web site in another browser, getting session II;
3) if property live.user.one.session.enabled is true, the system should be able to kill session I automatically.