Use AccountGroup.UUID instead of Account.Id

By switching to the UUID we can have a globally unique identifier
for group membership throughout the server, even if group information
comes in from a different data source.

Change-Id: Icb49d6a6aff8e62864ac0f78ceedbe03f01de894
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-server/src/test/java/com/google/gerrit/server/mail/FromAddressGeneratorProviderTest.java

@@ -278,7 +278,7 @@ public class FromAddressGeneratorProviderTest extends TestCase {
     account.setFullName(name);
     account.setPreferredEmail(email);
     final AccountState s =
-        new AccountState(account, Collections.<AccountGroup.Id> emptySet(),
+        new AccountState(account, Collections.<AccountGroup.UUID> emptySet(),
             Collections.<AccountExternalId> emptySet());
     return s;
   }