Early Startup of ModelerCore is problematic

* Use of an early startup class in the ModelerCore plugin clashes with
  startup processes in ModelerCore.start(). Result of this is tests can
  hang or take a long time to complete!

* TeiidServerManager
 * Scrapping the early startup class means the manager is lazily loaded
   when something first requests it. Thus, more processes need to be
   moved after its restoration. This includes the PreviewManager, which
   uses the manager default server version when creating preview jobs on
   its initialisation.