[Echo.Events] clear a context structure when handlers and contexts are empty
[Echo.Events] several improvements:
 - do not init a context structure in case of event publishing;
 - checking contexts structure for emptyness in case of handlers execution.
[Stream control] destroy item in case of delete action;
 - apply structure update in appropriate way in case of item destroying (do not destroy item before animate);
 - destroy items in case of stream destruction
[Stream control] do not store an item as a free variable inside _smileys.tag function scope
[Submit control] unsubscribe from posting subscriptions in case of submit control destroying
[Echo.Control] avoid memory leak issues via removing context variables which can be stored as free variables to function scope