* use ES6 import / export
* UTILS: export individual utilities
* TESTS: localize TestHelper includes
BREAKING CHANGE:
* all utilities export independent functions
* library sources got ported to ES6. You must now use
a ES module bundler such as Browserify + babelify or
Webpack to consume this library (or parts of it).
This introduces a 'property.clone' event that allows
plugging into the cloning mechanism when cloning
nested extension elements.
Related to camunda/camunda-bpmn-moddle#35