Switch out an ArrayList with CopyOnWriteArrayList
Added a delete-by-key to OnmsDao.
Changed "undefined" to "localhost" as the default value of distPoller to
partially address bug NMS-5750.
Moved and renamed SimpleTopologyProvider to SimpleGraphProvider so that
it can be subclassed by the VmwareTopologyProvider. Cleaned up the
commented-out sections of the simple provider's blueprint.xml.
Added Vaadin Container classes that can wrap OnmsDao classes to easily
display DAO beans in the UI. Removed unused UnDoer class.