Moving test_user_dev->user_dev in plugin app configs & adding plugin static serving

Moving test_user_dev->user_dev in plugin app configs & adding plugin static serving

The test_user_dev (as opposed to user_dev) was a legacy before we had
each application running in its own directory (as they now do in
pytest).  Move that name to just user_dev... this is more consistent
with the rest of our naming and will make writing these config files
easier.  (If we want to test that changing these still works, that
should be a separate unit test with special config files.)

Additionally, add plugin static serving to the common test paste
config file.

This commit sponsored by Juan Jose Marin Martinez.  Thank you!