Implement support for observedproperty and DataOutput QML elements

Implement support for observedproperty and DataOutput QML elements (and corresponding C++ API) in the OpenGL Runtime. Initially it is sufficient to create a DataOutput from each DataInput entry as that can be added from the viewer.

• Add DataOutput nodes that receive “valueUpdated” signal as a marked value is change in the presentation by the engine.
• Change UIA & UIP parsing to accept “observedproperty” as XML attribute in addition to “controlledproperty” and make it create a DataOutput model object from that. This is for adding future support in the editor.
• Change UIA & UIP parsing to create DataOutput model object from each "controlledproperty" for now in Qt 3D Studio 2.4 version. Optimally the DataOutput shouldn’t be by default created from DataInput nodes, but as we need a change that “just works” without editor changes making the parser generate both nodes for each DataInput in UIA and each “controlledproperty” for now is the only way (beyond hacking a asynchronous getAttribute API that then breaks as presentations are modified).