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 introduces a clean separation of node and browser tests.
ALL tests should be organized according to where they are run
non browser (áka node tests): `test/spec/node`
browser tests: `test/spec/browser`