- Recorded the fix in changelog.
- Added a separate screen to show the unmigration instruction, which
  makes it easier for people to find it than search logs.

This should work across builds and even across jobs, and does not force us to load other builds.

Add pom.xml.versionsBackup and .DS_Store to .gitignore

Making side-panel and main-panel absolute positioned and full height

[FIXED JENKINS-25989] Allow breaking label and node lists

[FIXED JENKINS-26155] Fix Hungarian build index page while building

Was using JS to size panels. This change only effects screens > 768px. Less than 768px is responsive.

ItemsTest.moveItem showed that if migrate is called on a nonexistent directory, we should do nothing.

#1406 silently skipped the call to moveDirectory in case newBuildDir.isDirectory(), rather than throwing an IOE as renameTo does.
Also deleting apparently useless call to forceMkdir.