[JENKINS-56152] Improve plugin manager UI wording + [JENKINS-56173] - Fix...

[JENKINS-56152] Improve plugin manager UI wording + [JENKINS-56173] - Fix JavaScript error in Plugin Manager when optional dependency metadata cannot be retrieved (#3904)

* [JENKINS-56173] Uncaught TypeError: Cannot read property 'jenkinsPluginMetadata' of undefined

* [JENKINS-56173] missing dependencies covers both not installed and not enabled

* [JENKINS-56152] i18n: DirectlyDependentPlugins.title / IndirectlyDependentPlugins.title

* [JENKINS-56152] replace `version X` with `(X)`

* [JENKINS-56152] simplify messages; replace `version X` with `(X)`; use higher instead of later

* [JENKINS-56173] Uncaught Exception: TypeError: Cannot read property 'get' of undefined at _createResponder

* Update PluginWrapperTest

* Switch to descriptive class for plugin version