Make it run with Qt6

This is a huge commit. Changes:
* Obviously, make it compile
* Make it run (only scarcely tested)
* get rid of most of clang's warnings

Let's see what surprises are in store...

1 files changed, 1 insertions, 1 deletions

diff --git a/mappingtreeproxy.h b/mappingtreeproxy.h
index 158cde9..0ee6f40 100644
--- a/mappingtreeproxy.h
+++ b/mappingtreeproxy.h
@@ -22,7 +22,7 @@ class MappingTreeProxy : public QSortFilterProxyModel {
         virtual bool filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const;
 
     private:
-        QRegExp mFilter;
+        QRegularExpression mFilter;
 };
 
 #endif // MAPPINGTREEPROXY_H