[JENKINS-43786] Overhaul of Manage Jenkins page (#2857)

* [JENKINS-43786] Initial source code modifications

* [JENKINS-43786] Adding a customized Bootstrap version and some messages were adapted

* [JENKINS-43786] Some Monitors included in the core have been adapted

* [JENKINS-43786] Reverting an unexisting typo

* [JENKINS-43786] Applying final styles

* [JENKINS-43786] Addressing more use cases

* [JENKINS-43786] Revisiting how the buttons are shown

* [JENKINS-43786] Adjustments in the administrative monitor pop-up

* [JENKINS-43786] Added more use cases related with administrative messages

* [JENKINS-43786] Adapted the Administrative Monitors provided by Jenkins core

* [JENKINS-43786] Addressed the @daniel-beck's review

* [JENKINS-43786] Wrong indent

* [JENKINS-43786] Better semantic HTML

* [JENKINS-43786] Better semantic HTML

* [JENKINS-43786] Applying the same criteria for listing items

* [JENKINS-43786] Adapted tests

* [JENKINS-43786] Removing redirect links in the administrative monitor descriptions

* [JENKINS-43786] Adapted Administrative Monitor

* [JENKINS-43786] Reverted Redirect URLs

* [JENKINS-43786] Applying the same code style

* [JENKINS-43786] Applying the same code style

* [JENKINS-43786] Apply a common HTML markup to the Administrative Monitors in core

* [JENKINS-43786] One more Administrative Monitor updated

* [JENKINS-43786] Polishing some details

* [JENKINS-43786] Deprecating CSS Styles

* [JENKINS-43786] We are ready for deprecating anything

* [JENKINS-43786] We are ready for deprecating anything

* [JENKINS-43786] Details