fixes bug #84 - gridster-resized event not passed to gridsterItems' scope

Best I can tell, the scope of custom gridsterItems is a sibling of the scope that the `gridster-resized` event is $broadcast on... so it never reaches the gridsterItems' scope.  $broadcasting the event on gridster's scope's `scope.$parent` scope instead allows the event to be caught where it needs to be. 

Also, the logic in the `updateResizableDimensions()` function seems to be off, causing the `enabled` variable to evaluate to `true` no matter what