Add kra and ora imageio plugins (read-only)

kra is the native format for Krita and ora the interchange format
for krita, gimp and mypaint (it's also mypaint's native format).
Both formats are simply zip containers with an embedded png.

REVIEW:126675

src/imageformats/kra.cpp

@@ -0,0 +1,88 @@
+/* This file is part of the KDE project
+   Copyright (C) 2013 Boudewijn Rempt <boud@valdyas.org>
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the Lesser GNU General Public
+   License as published by the Free Software Foundation; either
+   version 2 of the License, or (at your option) any later version.
+
+   This code is based on Thacher Ulrich PSD loading code released
+   on public domain. See: http://tulrich.com/geekstuff/
+*/
+
+#include "kra.h"
+
+#include <kzip.h>
+
+#include <QImage>
+#include <QIODevice>
+#include <QFile>
+
+KraHandler::KraHandler()
+{
+}
+
+bool KraHandler::canRead() const
+{
+    if (canRead(device())) {
+        setFormat("kra");
+        return true;
+    }
+    return false;
+}
+
+bool KraHandler::read(QImage *image)
+{
+    KZip zip(device());
+    if (!zip.open(QIODevice::ReadOnly)) return false;
+
+    const KArchiveEntry *entry = zip.directory()->entry(QLatin1String("mergedimage.png"));
+    if (!entry || !entry->isFile()) return false;
+
+    const KZipFileEntry* fileZipEntry = static_cast<const KZipFileEntry*>(entry);
+
+    image->loadFromData(fileZipEntry->data(), "PNG");
+
+    return true;
+}
+
+bool KraHandler::canRead(QIODevice *device)
+{
+    if (!device) {
+        qWarning("KraHandler::canRead() called with no device");
+        return false;
+    }
+
+    char buff[57];
+    if (device->peek(buff, sizeof(buff)) == sizeof(buff))
+        return qstrcmp(buff + 0x26, "application/x-krita") == 0;
+
+    return false;
+}
+
+QImageIOPlugin::Capabilities KraPlugin::capabilities(QIODevice *device, const QByteArray &format) const
+{
+    if (format == "kra" || format == "KRA") {
+        return Capabilities(CanRead);
+    }
+    if (!format.isEmpty()) {
+        return 0;
+    }
+    if (!device->isOpen()) {
+        return 0;
+    }
+
+    Capabilities cap;
+    if (device->isReadable() && KraHandler::canRead(device)) {
+        cap |= CanRead;
+    }
+    return cap;
+}
+
+QImageIOHandler *KraPlugin::create(QIODevice *device, const QByteArray &format) const
+{
+    QImageIOHandler *handler = new KraHandler;
+    handler->setDevice(device);
+    handler->setFormat(format);
+    return handler;
+}