Improve support of notifications attachment

[Roman Sakno]

Not all connectors and adapters supports handling of SNAMP notifications attachments. But this is the only way to organize end-to-end monitoring and correlation management using SNAMP.

[Roman Sakno]

Greatly improved information model of Notification object. The major improvements: 1. Notification attachment is not a dictionary, it may be any object 2. Notification attachment type can be supplied in two ways: static typing (attachment type is known BEFORE any notification received via NotificationMetadata.getAttachmentType()) and dynamic typing (Notification.getAttachment() may return an instance of ManagedEntityValue which holds the attachment and its type) 3. Notification may contain correlation identifier 4. Notification may have a chain of correlated notifications (see Notification.getNext()). This method designed for future purposes when connectors became so smart for automatic correlation.

[Roman Sakno]

Closes #28

→ <<cset f5185408261f>>

[Roman Sakno]

Closes #28

→ <<cset f5185408261f>>