Good progress toward an interface which doesn't require the Update Ports button. There are still some very broken things here, though.
Fixed issue with moving fiducials in and out of hierarchies. However, there are still problems when trying to remove a hierarchy. I'm probably gonna trash this branch and try something else.
Can now add individual ports to a table, remove them, change their visibility, and their fiducials' names.
ENH: User can now change the shapes and orientations of individual tubes within the Port Placement module.
ENH: Extension now does not require any changes to current Slicer code.

In initializing the qMRMLTransformSliders widget, I'm now making use of the Q_PROPERTY mechanism which is already built into Slicer.