isLoggedIn method of EcmAuth client is returning "true" when ticket expires

[chris-equis]

Type of issue: (check with "[x]")

- [ ] New feature request
- [x] Bug  
- [ ] Support request

Current behavior:

calling isLoggedIn() returns true if the ticket is expired

Expected behavior:

calling isLoggedIn() should return false if the ticket is expired

Steps to reproduce the issue:

1. Use EcmAuth instance to login with valid credentials
2. Check that the ticket-ECM key was registered in LocalStorage and it has stored the ticket
3. Wait until the ticket expires or modify (not delete) the ticket directly in LocalStorage
4. console.log(instance.isLoggedIn()) returns true because it just checks that there is a ticket but not its validity

[eromano]

In the alfresco-js-api is already present validateTicket() method that checks the ticket against the server and returns a promise.

Change now the isLoggedIn in this way could have two side effects:

• too many calls against the server
• breaking change with the firm of the actual isLoggedIn

We could think a way to check the token if is still valid and invalidate the localstorage after some events as 401