Session Tracking Customizations

The servlet engine automatically chooses the method to use (first cookies, then re-writing).
Sessions expire if user does not click on anything. Default is 30min. Change it in web.xml or with
```
public void HttpSession.setMaxInactiveInterval(int secs);
```
set with care (security vs resource use).

Other helpful methods are


//Has this session just been created?
public boolean HttpSession.isNew();

//Invalidate session
public void HttpSession.invalidate();

//When was it created?
public long HttpSession.getCreationTime();