feat(core/EventBus): adapt w3c defaultPrevented

This aligns our event layout with the w3c dom events, signaling default
prevented via a defaultPrevented property.
fix(move/DragSupport): clean up on diagram destroy
fix(util/Event): stop propagation and default
fix(context-pad): dispatch original events
chore(move/Draggable): remove unused code
asd
feat(modeling): create shape outside commands

We now create shapes outside of create commands.

This makes advanced customizations on the added shapes possible.
fix(core/Canvas): ignore non-existing gfx in add/removeMarker
chore(features/dragging): extract general dragging util

This commit replaces the existing drag implementations with a more
versatile one that can easily be mocked during scripting.
chore(RuleProvider): allow registration for multiple rules
feat(create): implement basic create module

Related to bpmn-io/bpmn-js#137
feat(snapping): snap create

Related to bpmn-io/bpmn-js#137
chore(Resize): port to new dragging infrastructure