[fix] fixed some quirks with plugins

includes:
  * added default values for plugin related properties (credits go to
    @dacrome)
  * loading plugin after bean initialization
  * fail deployment when 'plugin.enabled' is 'true' but 'plugin.jar.path'
    or 'plugin.classname' are not set
  * added 'NoopPlugin' as default plugin
  * added default properties to
    'src/main/deploy/addon-self-administration.properties'