Improve album cover loader, lyrics search and streaming support

- Improve album cover loader
- Add album cover loader result struct
- Move album cover thumbnail scaling to album cover loader
- Make init art manual look for album cover images in song directory
- Make album cover search work for songs outside of collection and
  streams
- Make album cover search work based on artist + title if album is not
  present
- Update art manual in playlist for local files, devices and CDDA
- Make lyrics search work for streams
- Add stream dialog to menu
- Remove dead code in InternetSearchModel
- Simplify code in InternetSearchView

src/dialogs/addstreamdialog.h

@@ -0,0 +1,51 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2020, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef ADDSTREAMDIALOG_H
+#define ADDSTREAMDIALOG_H
+
+#include <QDialog>
+#include <QString>
+#include <QUrl>
+#include <QLineEdit>
+
+#include "ui_addstreamdialog.h"
+
+class AddStreamDialog : public QDialog {
+  Q_OBJECT
+
+ public:
+  AddStreamDialog(QWidget *parent = nullptr);
+  ~AddStreamDialog();
+
+  QUrl url() const { return QUrl(ui_->url->text()); }
+  void set_url(const QUrl &url) { ui_->url->setText(url.toString());}
+
+ protected:
+  void showEvent(QShowEvent*);
+
+ private slots:
+  void TextChanged(const QString &text);
+
+ private:
+  Ui_AddStreamDialog *ui_;
+
+};
+
+#endif  // ADDSTREAMDIALOG_H