updates German translation

Since 'Job' was renamed to 'Item', this translation should be updated
Update sidepanel_de.properties
Update newJob_de.properties
Return correct URL to Jenkins master node
Use full display name by default for model links to Items
[FIXED JENKINS-17667] - Syncronization of InstallerTranslator::getToolHome()

There appears to be some unthreadsafe initialization going on here.
Initialize/get inside a synchronized block for threadsaftey.
Fix changelog generation in ExtractResourceWithChangesSCM
when several files are changed at once
(used in the fix for JENKINS-22622)
Update newJob_de.properties
[FIXED JENKINS-23294] Interpret X-Forwarded-Port

- Also fixed handling of X-Forwarded-Proto and added support for X-Forwarded-Host

- Additional complexity is that there can be multiple headers with the same name (which was handled by default by accident) and
  that a header value may contain a comma separated list if there were multiple forwarding hops.
[FIXED JENKINS-23294] Deal with X-Forwarded-Port.
If this is set, use it instead of ServletRequest.getServerPort() for purposes of getRootUrlFromRequest().
Also treat the default port as scheme-specific in that method (which presumes that we in fact got the reported port right).
And enhance the reverse proxy setup monitor to validate that the Referer header (/manage)
actually matches what we have computed from getRootUrlFromRequest;
if it does not, something is messed up, though it may require some digging to find what.
(Would be better to let the monitor specify the exact problem it determined,
though this is not always actually possible;
for example if you are missing AllowEncodedSlashes NoDecode in Apache,
you just get a 404 from Apache without even getting to Jenkins.)
[FIXED JENKINS-23294] Interpret X-Forwarded-Port

- Also fixed handling of X-Forwarded-Proto and added support for X-Forwarded-Host

- Additional complexity is that there can be multiple headers with the same name (which was handled by default by accident) and
  that a header value may contain a comma separated list if there were multiple forwarding hops.
Since the javadoc for the method says that the relative path should start without a leading '/' strip any leading '/' characters

- I had been tempted to throw IllegalArgumentException but that would break a lot of tests
Somebody did not read the javadoc for the goTo method (urls not supposed to start with a /)
Reuse Computer.getUrl() for ModelHyperlinkNote and getSearchUrl()s
Break links inside pre tags

to prevent page from horizontal scrolling.
Update style.css
[FIXED JENKINS-23683] Check whether war's directory is writable
Merge pull request #1294 from jenkinsci/pull/1265/head

[FIXED JENKINS-23294] Interpret X-Forwarded-Port
Merge pull request #1253 from daniel-beck/ModelHyperlinkNote-MasterNode

Return correct URL to Jenkins master node
Merge pull request #1311 from daniel-beck/JENKINS-23683

[FIXED JENKINS-23683] Check whether war's directory is writable