Move "implements CrawlUriReceiver" from WorkQueueFrontier to superclass

AbstractFrontier where the method CrawlUriReceiver.receive() is implemented.

engine/src/main/java/org/archive/crawler/frontier/AbstractFrontier.java

@@ -51,6 +51,7 @@ import java.util.regex.Pattern;
 
 import org.apache.commons.httpclient.HttpStatus;
 import org.apache.commons.httpclient.URIException;
+import org.archive.crawler.datamodel.UriUniqFilter.CrawlUriReceiver;
 import org.archive.crawler.event.CrawlStateEvent;
 import org.archive.crawler.framework.CrawlController;
 import org.archive.crawler.framework.Frontier;
@@ -87,6 +88,7 @@ public abstract class AbstractFrontier
                SeedListener, 
                HasKeyedProperties,
                ExtractorParameters,
+               CrawlUriReceiver,
                ApplicationListener {
     private static final long serialVersionUID = 555881755284996860L;
     private static final Logger logger = Logger

engine/src/main/java/org/archive/crawler/frontier/WorkQueueFrontier.java

@@ -52,7 +52,6 @@ import java.util.regex.Pattern;
 
 import org.apache.commons.collections.iterators.ObjectArrayIterator;
 import org.archive.crawler.datamodel.UriUniqFilter;
-import org.archive.crawler.datamodel.UriUniqFilter.CrawlUriReceiver;
 import org.archive.crawler.event.CrawlURIDispositionEvent;
 import org.archive.crawler.framework.ToeThread;
 import org.archive.crawler.frontier.precedence.BaseQueuePrecedencePolicy;
@@ -83,7 +82,6 @@ import com.sleepycat.je.DatabaseException;
  */
 public abstract class WorkQueueFrontier extends AbstractFrontier
 implements Closeable, 
-           CrawlUriReceiver, 
            ApplicationContextAware {
     private static final long serialVersionUID = 570384305871965843L;