MVF — Clarify uri vs refrence vs externalReference

The terms may be confusing, and implementers may 'misplace' important pieces of information

'uri' is meant to be an 'individual/instance' URI, that identifies the entity represented by the MVF element
(e.g. an individual Community - mapped by a mvf:Community, or an individual Concept - mapped by a mvf:MVFEntry)

'externalReference', which only applies to MVFEntry, may be better called 'semanticReference', and be exepcted to resolve to a definitional resource such as an ontology (class/expression)

'reference' seems to hold more descriptive/informative links such as web pages or other web resources.
Maybe it could be called 'descriptiveReference' - in contrast with 'semanticReference'?

Rename properties as proposed

Rename MVFEntry::externalReference to semanticReference
Rename MVFElement::reference to descriptiveReference

Update the metamodel and ontology diagrams and document text referencing these names, as given below in Revised Text.