FELIX-3947 Fix ClassDefNotFoundError if Servlet API cannot be wired

* Move Web Console Plugin registration from DefaultWebConsolePlugin
  class (static method with DefaultWebConsolePlugin creation) to
  InventoryPrinterManagerImpl
* Define constants for the DefaultWebConsolePlugin in ConsoleConstants
  to prevent loading the class

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1452205 13f79535-47bb-0310-9956-ffa450edef68