DMN12 — FEEL versions cannot be distinguished

FEEL has changed between DMN 1.0, 1.1 and 1.2. We need a way to know which version is used in a model, e.g. by using a new URI for expressionLanguage and typeLanguage.

This is also important, in case FEEL is used outside DMN, because in that case the surrounding model doesn't have any reference to a DMN version.

New URI for FEEL 1.2

In accordance with the "OMG Policy for Versioning of Specification URIs, File URIs, and XML Namespaces in OMG Specifications – Version 2" (smsc/2015-3-06) and the DMN 1.2 namespace URIs introduced together with Diagram Interchange, new namespace should be:
http://www.omg.org/spec/DMN/20180521/FEEL/