title: can't detect touch on CCNode - cocos2d v3.0
body: <p>I have recently started to explore cocos2d v3.0. I'm trying some basic stuff but having some trouble.</p>
  
  <p>Basically I'm Subclassing a CCSprite to create Square object. After that adding the square object to  my HelloworldScene and I wanna receive touches on my Square sprite. For some reason it's not working.</p>
  
  <p>Here's the code
  --header file</p>
  
  <pre><code>#import "CCSprite.h"
  @interface Square : CCSprite
  @end
  
  implementaion file
  
  #import "Square.h"
  #import "cocos2d.h"
  @implementation Square
  -(id)init {
      // Apple recommend assigning self with supers return value
      self = [super init];
      if (!self) return (nil);
      self.contentSize = [[CCDirector sharedDirector] viewSize];
      self.userInteractionEnabled = YES;
      return self;
  }
  -(void)touchBegan:(UITouch *)touch withEvent:(UIEvent *)event
  {
      CCLOG(@"touch received");
  }
  @end
  </code></pre>
  
  <p>and here's the hello world <code>init</code> method</p>
  
  <pre><code>- (id)init
  {
      // Apple recommend assigning self with supers return value
      self = [super init];
      if (!self) return(nil);
  
      Square *_square = [[Square alloc] initWithImageNamed:@"background.png"];
      [_square setPosition:CGPointZero];
      [self addChild:_square];
      // done
  return self;
  }
  </code></pre>
  
  <p>when I run the code I can see the sprite on the screen but when I tap on it nothing happens the touch began never gets called. What am I missing here ? </p>