[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
[Echo.Events] several fixes:
 - execute callback for deeepest context even if the context doesn't exists (call it with the empty object to indicate this situation);
 - remove parent context in case it is empty.
[Echo.Events] avoid unnecessary handler deletion
[Echo.Events -> Tests] add several test cases:
 - check subscription structure after event publishing;
 - check that parent context deleted after child unsubscribed if the particular parent context is empty;
 - check that if child's context has the same name as a parent's, this doesn't cause error context creation.\Update test subscription structure.
[Stream control] destroy parent item after children
[Stream control] generate smiley tag only ones
[Echo.Control] minor code updates
[Echo.Control] add comment to avoid ambiguity
[Echo.Events] avoid clearing contexts in case of undefined handler id and defined context; update default value for contexts structure
[Echo.Control] update comment