Allow showing sub-flow entry/exit binding nodes as normal nodes

[JuanKUYang]

When the sub-flow is viewed in full-screen the entry and exit binding nodes are shown as half circles at the edge of the viewport.
Hope they could be shown as normal nodes.

[JuanKUYang]

Hi @vlad-bunescu ,
Please help to provide images for entry and exit binding nodes. Thanks!

[matthoward366]

@JuanKUYang I don't think elyra would provide these node images. They would come from the pipeline-flow and would be up to the consuming application to provide. Same as node images.