Fetch validator lists from remote sites:

Validator lists from configured remote sites are fetched at a regular
interval. Fetched lists are expected to be in JSON format and contain the
following fields:

* "manifest": Base64-encoded serialization of a manifest containing the
  validator publisher's master and signing public keys.

* "blob": Base64-encoded JSON string containing a "sequence",
  "expiration" and "validators" field. "expiration" contains the Ripple
   timestamp (seconds since January 1st, 2000 (00:00 UTC)) for when the
  list expires. "validators" contains an array of objects with a
  "validation_public_key" field.

* "signature": Hex-encoded signature of the blob using the publisher's
  signing key.

* "version": 1

* "refreshInterval" (optional)

src/test/unity/app_test_unity.cpp

@@ -45,5 +45,6 @@
 #include <test/app/TrustAndBalance_test.cpp>
 #include <test/app/TxQ_test.cpp>
 #include <test/app/ValidatorList_test.cpp>
+#include <test/app/ValidatorSite_test.cpp>
 #include <test/app/SetTrust_test.cpp>
 #include <test/app/Ticket_test.cpp>