Added server functionality

RegisterServlet.java
* Implemented it to accept a register request and responds appropriately with JSON.

BaseServlet.java
* Provided Comments on helper methods available
* Fixed setSuccess to be more flexible.

UserManager.java
* Wrote skeleton class for managing users in the server
* This class is to be implemented

.gitIgnore
* Updated to ignore the ROOT directory if a local maven build is done locally

pom.xml
* Added the JSON dependency

BY: colinkho