Jenkins 2.375.4

What's new in this version:

Changes since 2.375:
- Prevent potential deadlocks on websocket agents
- Fix Gravatar error on profile page (regression in 2.335)
- Add telemetry for activation of permissions that are not enabled by default

Notable changes since 2.361.4:
- Update to various UI elements. Modernize icons, navigation, and buttons
- Improve breadcrumb bar accessibility
- Update the design of notifications
- Update the weather and status icons
- Prevent a stack overflow when loading a queue (regression in 2.361)
- Winstone 6.4: Upgrade Jetty from 10.0.11 to 10.0.12. Remove support for OpenSSL-style PEM-encoded RSA private keys when running Jenkins with the embedded Jetty (Winstone) container and TLS. The flags --httpsPrivateKey and --httpsCertificate have been removed. Support HTTP/2 without the use of a custom --extraLibFolder option6.2 changelog, Winstone 6.3 changelog, Winstone 6.4 changelog, Jetty 10 and 11 blog post, Jetty 10.0.12 changelog, Documentation, Remove ability to load pem cert for winstone)
- Add sidebar to plugin manager, increase search bar size
- Add support for Apple's touch bar icons
- Removed: The signed jenkins-parent-${JENKINS_VERSION}-src.zip source archives have been removed from Artifactory for future releases. Users who wish to download source archives for offline consumption are encouraged to do so via GitHub
- Display email form validation errors near the data entry field in the setup form
- Show recommended actions (e.g., to update affected plugins) in security warnings popup
- Clarify safe restart won't wait for Pipeline jobs
- Allow form checker to check more than one thing at a time
- Add documentation for the --paramsFromStdIn and --version command-line options
- Fix sorting of British currency in tables
- Improve build progress animation when refreshing parts of the history/executors widget
- Fix the resize behavior of Execute Shell build steps
- Fix searchBar is null issue in setup wizard and when using custom Jenkins headers
- Ensure that temporary network partitions do not cancel the WebSocket ping thread (regression in 2.363)