This fixes a bug where updating the id property of an element
was not propagated to the diagram. Thus, retrieving the element
based on the new id from diagram-js did not work.
Closes#238
This adds the modeling#updateProperties(element, props) method to the
modeler that can be used to set BPMN 2.0 properties on elements.
By assigning the properties this way, the modeler is aware of the
elements that got changed and can update / redraw the elements
accordingly.
This hooks up with the modelers undo/redo chain, too.
Related to #167