Implementing configured discovery:

- added some additional error logging, useful during debugging.
Implementing configured discovery:

- Added some additional useful constants.
Implementing configured discovery:

- use same configuration type and endpoint property as used in Amdatu
  Remote Services; this is something we should make configurable!
- give the endpoints a real unique ID (based on UUIDs);
- report back the error code of a proxied request to the calling
  proxy.
Implementing configured discovery:

- avoid duplicate imports of the same service;
- let the endpoint descriptor reader use a pre-created arraylist
  to allow us to properly define an equality function on it. This
  way, we can more easily lookup whether or not there are changes
  in the discovered endpoints.