Don't use Discogs if fetching all album covers because of trottling.

src/covermanager/coverprovider.h

@@ -39,10 +39,11 @@ class CoverProvider : public QObject {
   Q_OBJECT
 
 public:
-  explicit CoverProvider(const QString& name, QObject* parent);
+  explicit CoverProvider(const QString &name, const bool &fetchall, QObject *parent);
 
   // A name (very short description) of this provider, like "last.fm".
   QString name() const { return name_; }
+  bool fetchall() const { return fetchall_; }
 
   // Starts searching for covers matching the given query text.  Returns true
   // if the query has been started, or false if an error occurred.  The provider
@@ -56,6 +57,8 @@ signals:
 
 private:
   QString name_;
+  bool fetchall_;
+
 };
 
 #endif // COVERPROVIDER_H