delete subscription support

This adds support for deleteSubscription per id and update the API a bit so that the response object can be used.

It seems that the current code still has one issue: creating a subscription may return a list of response (per API documentation) so the SubscriptionResponse should probably move to a list of data instead of single instance.

Tested createSubscription, deleteSubscription(long id), deleteAllSubscription and getSubscriptionList based on tag subscription.