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.cpp

@@ -0,0 +1,54 @@
+/*
+ * 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/>.
+ *
+ */
+
+#include "addstreamdialog.h"
+#include "ui_addstreamdialog.h"
+
+#include <QSettings>
+#include <QUrl>
+#include <QLabel>
+#include <QLineEdit>
+#include <QPushButton>
+#include <QDialogButtonBox>
+#include <QShowEvent>
+
+AddStreamDialog::AddStreamDialog(QWidget* parent) : QDialog(parent), ui_(new Ui_AddStreamDialog) {
+
+  ui_->setupUi(this);
+
+  connect(ui_->url, SIGNAL(textChanged(QString)), SLOT(TextChanged(QString)));
+  TextChanged(QString());
+
+}
+
+AddStreamDialog::~AddStreamDialog() { delete ui_; }
+
+void AddStreamDialog::showEvent(QShowEvent*) {
+
+  ui_->url->setFocus();
+  ui_->url->selectAll();
+
+}
+
+void AddStreamDialog::TextChanged(const QString &text) {
+
+  QUrl url(text);
+  ui_->button_box->button(QDialogButtonBox::Ok)->setEnabled(url.isValid() && !url.scheme().isEmpty() && !url.host().isEmpty());
+
+}