QmlDesigner: Move QDS mime types to constants

Also:
- Rename libraryresource to asset to match the assets view name.
- Replace the outdated "bauhaus" name with "qtdesignstudio".

Change-Id: I4cacfdc33c029431b1a7b906439dabc3d9a7ee26
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/components/itemlibrary/itemlibrarymodel.cpp

@@ -36,6 +36,7 @@
 #include <nodemetainfo.h>
 #include <projectexplorer/project.h>
 #include <projectexplorer/session.h>
+#include "qmldesignerconstants.h"
 #include "qmldesignerplugin.h"
 #include <utils/algorithm.h>
 #include <utils/qtcassert.h>
@@ -512,9 +513,9 @@ QMimeData *ItemLibraryModel::getMimeData(const ItemLibraryEntry &itemLibraryEntr
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
     stream << itemLibraryEntry;
-    mimeData->setData(QStringLiteral("application/vnd.bauhaus.itemlibraryinfo"), data);
+    mimeData->setData(Constants::MIME_TYPE_ITEM_LIBRARY_INFO, data);
 
-    mimeData->removeFormat(QStringLiteral("text/plain"));
+    mimeData->removeFormat("text/plain");
 
     return mimeData;
 }