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
Nico Rehwaldt