Offline installer for jenkins editor plugin

[de-jcup]

At
https://marketplace.eclipse.org/comment/5885#comment-5885
a user wanted to have an offline installer for jenkins editor.

I had the same issue with bash editor a while ago - see
de-jcup/eclipse-bash-editor#110

At de-jcup/eclipse-bash-editor#110 a template for a local update site was added. This template can be reused for jenkins editor as well.
The only thing to change: replace the content of bash editor parts with corresponding stuff from
https://dl.bintray.com/de-jcup/jenkinseditor/
instead of
https://dl.bintray.com/de-jcup/basheditor/

Look into the template documentation (README.md) for details. Do the update tasks but replace https://dl.bintray.com/de-jcup/basheditor/
with
https://dl.bintray.com/de-jcup/jenkinseditor/
and of course the dedicated versions of jenkins editor.

If there are problems, please add a comment here.