Address user feedback: restart and no pending operation feedback

[fedorov]

From @cpinter:

So the only thing we learned is that Slicer needs to be restarted after installing the Python packages required by IDC (so install extension -> restart -> open the module -> click OK -> restart).
One comment I have if you permit is that there is no wait cursor or message or nothing after clicking the "Download and import into DICOM database" button, so the user may be confused if it works correctly or not.
And a relevant piece of information may be that I had SlicerHeart installed that also installed pandas. There was some conflict with that it seemed to me (but I'm no pip expert)

This is Windows.

[fedorov]

Following the discussion with @jcfr, related to Slicer/Slicer#7707.