[FIXED JENKINS-39404] Restore symmetry by adding removeAction and removeActions methods to Actionable

[JENKINS-39404] Clarify the lack of transaction support and consequent effect on concurrent operations

- cannot use a local variable as the optimization only applies while we have not found the action being added

- We cannot modify `replaceAction` to return the dirty flag, in fact most callers probably don't care... but if you do care, we now provide `addOrReplaceAction`
- Clarify the javadocs to reflect that these methods are not going to affect actions added by transient action factories

[JENKINS-39404] We cannot change these to return a boolean, but doesn't matter because they would always return `true`

I would need to use <A super Action> which would allow Object.class

[FIXED JENKINS-39404] Restore symmetry by adding removeAction and removeActions methods to Actionable

Update the detached version of Maven plugin to 2.14

We have to do it, because some extension points are being executed on slaves (e.g. https://github.com/jenkinsci/cygwin-process-killer-plugin/blob/master/src/main/java/com/synopsys/arc/jenkinsci/plugins/cygwinprocesskiller/CygwinProcessKiller.java - ProcessKiller EP gets propagated).

It's a follow-up to https://github.com/jenkinsci/jenkins/pull/2568

[JENKINS-39363,CID-1205051] - Prevent resource leak in hudson.XmlFile#readRaw() in the case of encoding issues. (#2518)

[JENKINS-39363,CID-1205051] - Prevent resource leak in hudson.XmlFile#readRaw() in the case of encoding issues.

[JENKINS-39232] Walk the DelegatingComputerLauncher instances when checking if JNLPComputerLauncher (#2602)

* [JENKINS-39232] Walk the DelegatingComputerLauncher instances when checking if JNLPComputerLauncher

* [JENKINS-39232] Add a system property to enable legacy plugins to continue to work until they get fixed

* [JENKINS-39232] Be more forgiving of plugins

* [JENKINS-39232] Yet more forgiveness of plugins but define the forward contract

* [JENKINS-39232] Provide diagnostics when this issue is encountered

- Since the failure of strict verification is an issue, we should log it as a warning always

* Add viewport meta tag

Enables better responsiveness on mobile devices

* fix: Use self-closing tag

* Remove minimum-scale for best accessibility

* [JENKINS-26940] Print message when installer isn't applicable

* [JENKINS-26940] Only print when none found, add test

* Load i18n resource bundles from plugins if not found in jenkins core

Signed-off-by: Thorsten Scherler <scherler@gmail.com>

* Issue 404 response for missing i18n resource bundles

Currently issues a 200 with an "error" response payload. This change still issues the error response payload, but also sets the HTTP response.

Signed-off-by: Thorsten Scherler <scherler@gmail.com>

* [JENKINS-35845] Fix test since we return now a 404

* [JENKINS-35845] add test for getting locale from plugin. fix comments from oleg.

* [JENKINS-35845] Fix description

* [JENKINS-35845] Update PR with comments from Oleg

* [JENKINS-35845] Add feedback from tom

* eslint - formating changes and fix offences

* eslint - formating changes and fix offences

* [JENKINS-35845] remove code concerning 404 response. Fix resourceBundle test by prevent NPE to happen

* [JENKINS-35845] Link to issue on which we introduced the test

[FIXED JENKINS-38960] Deprecate getIconFilePathPattern and switch to IconSpec

* [JENKINS-36871] Switch to the new JnlpProtocolHandler based implementation

Todo

- [ ] Restore the cookie behaviour (but done right this time)
- [ ] Perhaps investigate issuing clients with TLS certificates (but would require a UI for managing them)

* [JENKINS-36871] License headers and javadocs

* [JENKINS-36871] Restore cookie handling

* [JENKINS-36871] Integrating Agent discovery components

* [JENKINS-36871] Pick up remoting 3.0-SNAPSHOT

* [JENKINS-36871] Pick up newer snapshot

* [JENKINS-36871] Oleg wants to log an exception that cannot happen

Placate the JDK 9 compiler