Add missing support for DataInput and DataOutput elements

[nikku]

Is your feature request related to a problem? Please describe.

We do not properly support bpmn:DataInput and bpmn:DataOutput elements. Adding support would mean that users may model input and output specifications in a BPMN 2.0 compliant way.

Example diagram: data-input-output.bpmn

Describe the solution you'd like

bpmn:DataInput and bpmn:DataOutput elements

• have an editable label / name (Support DataInput and DataOutput labels #953)
• may be moved within its original container (the ioSpecification holder) (961 data input output move #962)
• may be created from DataObjects (via replace menu) Allow replacement of DataObjects with DataInput / DataOutput #674
• can be moved freely on the diagram
• must be connected via bpmn:DataInputAssociation and bpmn:DataOutputAssociation to activities
• may be copied with host element

The underlying structure (bpmn:InputOutputSpecification elements) must be maintained in the process. This is partly covered via #910 already.

Describe alternatives you've considered

Keep our modeling support limited to data objects.

Additional context

As a pre-requisite to this issue we must properly wire data associations (#910).

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Depends on #910