iOS7 additional validations & cleanup

[stepio]

I was also working on the iOS7 support, merged my work with mainline.

Source: https://developer.apple.com/library/ios/documentation/UserExperience/Reference/PassKit_Bundle

[stepio]

Additional validations for pass:

        // If appLaunchURL key is present, the associatedStoreIdentifiers key must also be present
        if (appLaunchURL != null && CollectionUtils.isEmpty(associatedStoreIdentifiers)) {
            validationErrors.add("The appLaunchURL requires associatedStoreIdentifiers to be specified");
        }
        // groupingIdentifier key is optional for event tickets and boarding passes; otherwise not allowed
        if (StringUtils.isNotEmpty(groupingIdentifier) && eventTicket == null && boardingPass == null) {
            validationErrors.add("The groupingIdentifier is optional for event tickets and boarding passes, otherwise not allowed");
        }