- Add GUI to base docker images (Ubuntu + Debian). This is done via an
  intermediate docker stage that creates the "plugins" directory and
  which is copied in the final stage. Entrypoint replaced to be able to
  start the GUI on port 9080 as well as run YottaDB.
- Fix build/run comments to be accruate, as the older ones were out of
  date (latest -> latest-master, remove UTF-8 [it's already default],
  add port option for GUI).
- Remove readline libraries: While I would like for readline to be
  available, we need a lot more packages to be installed in order for
  the unversioned .so to be available; but this image is supposed to be
  as small as possible. So, never mind.
- Fix libcurl packages in main Dockerfile. It was done incorrectly in
  commit f92ef46d (it added the libcurl
  for the YottaDB build stage, where it is not actually used--it should
  be added in two places: a dev library for the GUI build stag...