Add new Event object to uco-investigation

[sbarnum]

To support broader cyber investigation use cases, we should add a new Event object to uco-investigation.

The Event object would be a direct derivation of uco-core:ContextualCompilation.

It would be defined as "An occurence of some activity characterized by the observables indicating such action occured."

[sbarnum]

Event class derived from ContextualCompilation

• eventType(string — controlled vocabulary) (1)
  -- Specifies the type of event
  -startTime(xsd:datetime) (0..1)
  -- Specifies the time that the event started.
• endTime(xsd:datetime) (0..1)
  -- Specifies the time that the event ended.
• objects(UcoObject) (0..*)
  -- Specifies a reference to an object that is related to this event.
• eventAttribute(DictionaryEntry) (0..*)
  -- Specifies attributes of the event.
  -- This is a temporary catch all for other properties until they are deemed worthy of explicit property definition

DictionaryEntry is a dictionary structure type

• key_name (1)
• For an instance, only one of the following would be present
  -- Key_value(literal) (0..1)
  -- Object(UcoObject) (0..1)
  -- Dictionary(DictionaryEntry) (for nested dictionaries) (0..1)

[ajnelson-nist]

Closing as duplicated by #541 . Implemented in UCO 1.3.0.