Move remaining code to app module

There's still some stuff that could potentially go elsewhere but I think it's enough for now.

src/app/blurhashimageprovider.cpp

@@ -0,0 +1,31 @@
+// SPDX-FileCopyrightText: 2021 Tobias Fella <tobias.fella@kde.org>
+// SPDX-License-Identifier: LGPL-2.0-or-later
+
+#include "blurhashimageprovider.h"
+
+#include <QImage>
+#include <QString>
+
+#include "blurhash.h"
+
+BlurhashImageProvider::BlurhashImageProvider()
+    : QQuickImageProvider(QQuickImageProvider::Image)
+{
+}
+
+QImage BlurhashImageProvider::requestImage(const QString &id, QSize *size, const QSize &requestedSize)
+{
+    if (id.isEmpty()) {
+        return QImage();
+    }
+    *size = requestedSize;
+    if (size->width() == -1) {
+        size->setWidth(256);
+    }
+    if (size->height() == -1) {
+        size->setHeight(256);
+    }
+    auto data = decode(QUrl::fromPercentEncoding(id.toLatin1()).toLatin1().data(), size->width(), size->height(), 1, 3);
+    QImage image(data, size->width(), size->height(), size->width() * 3, QImage::Format_RGB888, free, data);
+    return image;
+}