Core: Backport 6.x realm changes

Make acessible all the info about current realm (e.g name) anywhere, not only realm id
Reduce the number of differences between the two branches

Original changes by Shauren

Partial port of bacc90b6baa34e6a194c93e5a7860d4041f08af7 and 63def8aa3291d0a6e5f83b289ad12c4c8a3cebd9

src/server/game/Server/WorldSocket.cpp

@@ -414,7 +414,7 @@ void WorldSocket::HandleAuthSession(WorldPacket& recvPacket)
 
     // Get the account information from the auth database
     PreparedStatement* stmt = LoginDatabase.GetPreparedStatement(LOGIN_SEL_ACCOUNT_INFO_BY_NAME);
-    stmt->setInt32(0, int32(realmID));
+    stmt->setInt32(0, int32(realm.Id.Realm));
     stmt->setString(1, authSession->Account);
 
     _queryCallback = std::bind(&WorldSocket::HandleAuthSessionCallback, this, authSession, std::placeholders::_1);
@@ -457,7 +457,7 @@ void WorldSocket::HandleAuthSessionCallback(std::shared_ptr<AuthSession> authSes
         return;
     }
 
-    if (authSession->RealmID != realmID)
+    if (authSession->RealmID != realm.Id.Realm)
     {
         SendAuthResponseError(REALM_LIST_REALM_NOT_FOUND);
         TC_LOG_ERROR("network", "WorldSocket::HandleAuthSession: Sent Auth Response (bad realm).");