Add the missing method setBlacklist(const QStringList&)

On top of that, make nextPostPage() Q_INVOKABLE so it can be used from
QML.

src/libdanbooru/danbooruservice.cpp

@@ -523,6 +523,21 @@ void DanbooruService::setBlacklist(const QSet< QString > &blacklist)
 
 }
 
+void DanbooruService::setBlacklist(const QStringList &blacklist)
+{
+
+    if (blacklist.isEmpty()) {
+        return;
+    }
+
+    m_blacklist.clear();
+
+    for (auto element : blacklist) {
+        m_blacklist.insert(element);
+    }
+
+}
+
 void DanbooruService::setBoardUrl(const QUrl& url)
 {
     m_url = url;