Implementing configured discovery:

- moved civetweb to separate utils package to allow sharing between
  the rsa_http implementation and discovery_configured implementation;
- fixed an issue with the creation of endpoint_descriptors from a map
  of properties: the framework UUID should be extracted from the given
  properties; also give a warning when trying to create incomplete
  endpoint descriptors;
- made the endpoint descriptor reader and writer conform the RSA v1.0
  specification: objectClass should always be an array and endpoint.
  service.id should always be a long value;
- added endpoint descriptor reader and writer to main code;
- disabled the test utilities for endpoint descriptor reader and
  writer with a preprocessor definition;
- added separate deployment for configured discovery;
- fixed the deployment of the SLP-based discovery example (endpoint
  was not correctly deployed);
- renamed the namespace used for the calculator example to
  `org.apache.celix.calc` as we should not pollute any non-
  owned namespace;
- removed some confusing log messages;
- let the webserver callback only handle POST messages and only read
  the message body if we can find a corresponding endpoint;
- in case the webserver cannot handle the message, let the default
  implementation take over and return a 404;
- fixed the JSON encoding/decoding of the proxy and endpoint to
  conform to the service interface (single-valued responses should
  be returned, not an array);
- better error handling in the proxy when given unexpected responses;
- fixed some memory leaks;
- expose service_tracker_destroy as API method;
- implemented most of the importing side of the configured discovery,
  needs some additional testing;
- the exporting side of the configured discovery is still to be
  implemented;
- added some additional error logging, useful during debugging;
- Added some additional useful constants;
- 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;
- 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;
- fixed a couple of problems in the endpoint poller;
- make sure that each published service gets an endpoint ID;
- implemented the server for published services, allowing other
  RSAs to query the exported services;
- Added TODO about the endpoint ID in the RSA SHM implementation.