Use new locations for depenencies hosted on BinTray

BinTray is shutting down on May 1, 2021. See https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/.

This affects us as well, as we obtain some dependencies from there. We should switch to the alternative download locations once they become available.

• Eclipse AsciiDoctor Editor

  We have in our Oomph setup:

          url="https://dl.bintray.com/de-jcup/asciidoctoreditor/"/>

  See https://github.com/de-jcup/eclipse-asciidoctor-editor/issues/333 for discussion of moving the binaries.

  New location is https://de-jcup.github.io/update-site-eclipse-asciidoctor-editor/update-site/. (release 2.3.0 is now present)

• Eclipse Checkstyle plugin

  We have in our Oomph setup:

          url="https://dl.bintray.com/eclipse-cs/eclipse-cs/${eclipse-checkstyle.version}/"/>

  See https://github.com/checkstyle/eclipse-cs/issues/279 for discussion on moving the binaries.

  New location is https://checkstyle.org/eclipse-cs-update-site. (release 8.41 is now present)

• jmini/geneclipsetoc maven plugin

  We have in releng/org.eclipse.escet.configuration/pom.xml:

              <!-- Bintray jmini maven plugins. For geneclipsetoc plugin. -->
              <id>bintray.jmini.maven</id>
              <url>http://dl.bintray.com/jmini/maven/</url>

  See https://github.com/jmini/geneclipsetoc/issues/1 for discussion of moving the binaries. (unlikely, project appears to be dead)

  There is now a fork at https://github.com/bsi-software/geneclipsetoc. Likely new location is https://bsi-software.github.io/geneclipsetoc. (no release yet)