Extend core constructs from a single base type

[johnwunder]

Most (all if you don't count Observable) of the STIX core constructs have a common set of fields: id, idref, timestamp, Title, Description, Short_Description, Handling, Information_Source, and maybe others. Does it make sense to extend them all from a common base type that defines these common fields?

This would simplify the model and make it clear that all of the properties are universal across all of the core constructs.

[sbarnum]

#372 is a duplicate of this issue and has now been closed.
It contains a single substantive comment that should be considered here