use snackbar to tell users that H@H client is required for this feature

app/src/main/java/com/hippo/ehviewer/client/EhEngine.java

@@ -30,6 +30,7 @@ import com.hippo.ehviewer.client.data.GalleryInfo;
 import com.hippo.ehviewer.client.data.PreviewSet;
 import com.hippo.ehviewer.client.exception.CancelledException;
 import com.hippo.ehviewer.client.exception.EhException;
+import com.hippo.ehviewer.client.exception.NoHAtHClientException;
 import com.hippo.ehviewer.client.exception.ParseException;
 import com.hippo.ehviewer.client.parser.ArchiveParser;
 import com.hippo.ehviewer.client.parser.FavoritesParser;
@@ -57,6 +58,8 @@ import org.jsoup.nodes.Document;
 import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import okhttp3.Call;
 import okhttp3.FormBody;
@@ -79,6 +82,8 @@ public class EhEngine {
     public static final MediaType MEDIA_TYPE_JSON = MediaType.parse("application/json; charset=utf-8");
     private static final MediaType MEDIA_TYPE_JPEG = MediaType.parse("image/jpeg");
 
+    private static final Pattern PATTERN_NEED_HATH_CLIENT = Pattern.compile("(You must have a H@H client assigned to your account to use this feature\\.)");
+
     public static EhFilter sEhFilter;
 
     public static void initialize() {
@@ -665,6 +670,11 @@ public class EhEngine {
             throw e;
         }
 
+        Matcher m = PATTERN_NEED_HATH_CLIENT.matcher(body);
+        if (m.find()) {
+            throw new NoHAtHClientException("No H@H client");
+        }
+
         return null;
     }