The new autoloader (Zeitwerk) introduced in Rails 6.0 expects a constant
whose name derive from the filename.

- the PDF to jpg convertion tests fail because of the ImageMagick
  policy:
    https://stackoverflow.com/questions/52998331/imagemagick-security-policy-pdf-blocking-conversion
  One test is skipped and the other can be partially skipped by not
  installing ghostscript.
- the other tests are related to changes in ruby-commonmarker: we have a
  newer version in Debian and it's known to cause problems
    https://www.redmine.org/issues/35892

gem2deb already depends on it for the B-D

Add lintian override until the next repack since the non-minified
sources are provided.

- remove bits about removed code (OpenID plugin, diff)
- update Debian packaging info (including missing past info according to
  git history)

- commonmarker
- deckar01-task_list
- html-pipeline
- net-*

Update to upstream version '5.0.0'
with Debian dir 29590b3f3f8fd6bf0f9645db61dc5798c3db78c8