Separating node template from node types

Currently NodeTemplate inherits NodeType per original design. We should separate NodeTemplate and NodeType and remove the inheritance per the latest review discussion,

Thomas:
Hm, I think I understand why you sub-class NodeType (I guess you want to inherit method), but NodeTemplate in TOSCA terms is not really a specialization of NodeType. It's a pretty different concept that points to a NodeType rather than being a NodeType.

Considering this difference, my gut feeling is we should not press both into an object inheritance relation in the code. If there is general re-usable code in both NodeType and NodeTemplate (can you give examples), we should maybe try to factor it out of NodeType for general re-use?

Matt:
Agree, the node template should link to the node type defn. and validate (the immutable) properties as defined there. This would necessitate a new python type to hold just the value the template author assigned to the property itself (and validate against the property of the same name's definition in the linked node type).