Add notifications of successfull operations

[alexvanin]

Notary-disabled environment produces notifications to initiate voting mechanism. However there is (almost) no notification to notify about operation success. It can be very useful for awaiting operations (such as awaiting for new container to show up) and for monitoring the whole network.

I suggest to add such notifications. Some useful events:

• container has been created
• container has been deleted
• container has changed eACL
• storage node has been registered as network map candidate
• storage node has changed its state

Notifications must be described in doc.go files.

This should be relevant after enabling notary. We can try to implement it already, but there might be some collision in notification names with notary-disabled notifications.