This commit removes the bpmn model specific parts that have been
outsourced to the project bpmn-io/bpmn-moddle.
In addition it removes BPMN 2.0 diagrams that were crafted
especially for tests of that functionality.
Closes#25
This commit upgrades the code base to the latest diagram-js changes and
adds a component called BpmnRegistry that can be used to retrieve a
certain BPMN/DI element from a shape/connection id.
Related to #19