Add a part to the document so we can d&d and insert layers again

BUG:305371

Note: we probably are leaking the part object, so I need to check that.

krita/ui/kis_import_catcher.cc

@@ -42,11 +42,13 @@
 #include "kis_selection.h"
 #include "kis_node_commands_adapter.h"
 #include "kis_group_layer.h"
+#include "kis_part2.h"
 #include <QMessageBox>
 
 struct KisImportCatcher::Private
 {
 public:
+    KisPart2* part;
     KisDoc2* doc;
     KisView2* view;
     KUrl url;
@@ -55,7 +57,10 @@ public:
 KisImportCatcher::KisImportCatcher(const KUrl & url, KisView2 * view)
         : m_d(new Private)
 {
-    m_d->doc = new KisDoc2(0);
+    KisPart2 *part = new KisPart2(0);
+    m_d->doc = new KisDoc2(part);
+    part->setDocument(m_d->doc);
+
     m_d->view = view;
     m_d->url = url;
     KoFilterManager manager(m_d->doc);