Update and fix checkstyle and javadoc plugins

[HeinrichAD]

This PR update the checkstyle and javadoc plugins. This PR is one part of #189.

Changes

• checkstyle mvn checkstyle:checkstyle mvn checkstyle:checkstyle-aggregate
  • 2.11 -> 3.1.2
  • Module LineLength outside TreeWalker Modul
  • delete RedundantThrows module, hence it was removed with version 6.2 see https://github.com/checkstyle/checkstyle/issues/473
  • sort in alphabetical order
• javadoc mvn javadoc:javadoc
  • 2.9.1 -> 3.3.1
  • fix documentation over classes It turns out that javadoc wants two stars at the beginning. Before: /* ... */ After: /** ... */
  • At least my compiler gives me warnings if I you @SuppressWarnings("serial") instead of @SuppressWarnings("SERIAL")
  • update links to use https if possible Note: License file also use https: https://www.gnu.org/licenses/gpl-3.0.txt
  • update project link http://plantuml.sourceforge.net -> https://plantuml.com
• README
  • remove travis CI badges and use new GitHub workflow badges
  • use own screenshot instead of ftomassettis one (same image different repository url)
  • fix typos also closes #165
  • adjust ducumentation about the non existing -readonly tag for docker also closes #182
  • add syntax highlighting as far as possible

[arnaudroques]

@HeinrichAD Thanks for your contributions. I let you resolve conflicts on README.md before merging :-)

[HeinrichAD]

@HeinrichAD Thanks for your contributions. I let you resolve conflicts on README.md before merging :-)

As requested. Done. :smile:

[arnaudroques]

As requested. Done. 😄

Well, the message "This branch cannot be rebased due to conflicts" is still there. Maybe we should use a new PR for this ?

[HeinrichAD]

As requested. Done. smile

Well, the message "This branch cannot be rebased due to conflicts" is still there. Maybe we should use a new PR for this ?

I can do this. Please give me some minutes.

This is how it looks at my site: