Added RegistrationIdServlet.java
* Handles a change of registration id for a user

Modified RequestParameters.java
* Added string constant used to retrieve new Registration ID

Modified web.xml
* Set Url pattern for RegistrationIdServlet.java

Modified UserManager.java
* Modified for debugging purposes.
Modified index.jsp
* Introduces chat real talk
Merge pull request #3 from colinkho/master

Implemented Unregister and ChangePassword functionality