Added DHT initialization task (see comments below):

Added DHT initialization task (see comments below):
- The DHT initialization task is for preparing the DHT (if not yet done) in a
  very early state ("virgin" state) and inserts/updates node's current data as
  the first entry. With this data the node "knowns" only itself, not even the
  upper nodes. They will be added later on.
- Renamed instance 'task' to 'task_handler' as it is always a task handler
  class
- Other minor improvements