This commit adds
* handling of bpmn update as command listeners
* label support
Related to bpmn-io/diagram-js#45
BREAKING CHANGE:
* rename bpmnModeling -> modeling to achive parity with diagram-js
This commit fixes the append node command by caching and reusing created
shapes and bpmn elements.
This ensures we do not invalidate actions that build on these element
references.
Related to #6