Improved error messages (OAuthFilter + exceptions) and added fields to EventSearchView.

1. Improved error messages.

  a. exception error messages now have a stack trace
  b. OAuth filter (non jersey) now outputs a json object on error

2. Replaced the following fields in EventSearchView
  private int numParticipants 
w/
  private int numAttending;  // Includes organizers + registered users.
  private int numRegistered;
  private int maxRegistrations;