Move lyrics providers to own thread

src/lyrics/azlyricscomlyricsprovider.cpp

@@ -17,7 +17,8 @@
  *
  */
 
-#include <QObject>
+#include <QApplication>
+#include <QThread>
 #include <QString>
 #include <QUrl>
 #include <QRegularExpression>
@@ -46,6 +47,8 @@ QUrl AzLyricsComLyricsProvider::Url(const LyricsSearchRequest &request) {
 
 QString AzLyricsComLyricsProvider::StringFixup(const QString &text) {
 
+  Q_ASSERT(QThread::currentThread() != qApp->thread());
+
   static const QRegularExpression regex_words_numbers_and_dash(QStringLiteral("[^\\w0-9\\-]"));
   return Utilities::Transliterate(text).remove(regex_words_numbers_and_dash).toLower();