- 
The app User object manages information about current application user. 
- 
This object is optional, and it is used when the app needs to authenticate the user. 
- 
The authentication provides data about user’s identity: a unique user ID or similar. 
- 
The user login and logout calls are managed by the app. 
- 
To access existing User object, use currentUser property: 
//If no login has been done
MOCAUser user = MOCA.getInstance().login(applicationUserId);
//User is already logged in
MOCAUser user = MOCA.getInstance().getUser();
User will persist across restarts
User will stay "Logged in" in MOCA SDK until you explicitly call the logout method
- To logout a user, call:
user.logout()
- The user object holds a collection of properties. Property-value pairs can be set and retrieved.
- Each user object is persisted both locally and in the cloud.
- It is recommended to perform as many sets as desired and then
 just invoke a single save operation to persist them to the MOCA cloud.
user.setProperty("is_tester", true);
user.setProperty("gender", "male");
user.setProperty("height", 175.2);
user.setProperty("dateOfBirth", 0);
user.save(new MOCACallback<MOCAUser>() {
  @Override
  public void success(MOCAUser user) {
  }
  @Override
  public void failure(MOCAException error) {
  }
});
