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, 6 insertions, 2 deletions

diff --git a/mappingtreeproxy.cpp b/mappingtreeproxy.cpp
index 077d72a..6758f55 100644
--- a/mappingtreeproxy.cpp
+++ b/mappingtreeproxy.cpp
@@ -11,12 +11,16 @@
 MappingTreeProxy::MappingTreeProxy(QObject *parent) : QSortFilterProxyModel(parent) {}
 
 void MappingTreeProxy::setFilter(const QString &filter){
-    mFilter = QRegExp(filter);
+    if(!filter.isEmpty()){
+        mFilter = QRegularExpression(filter);
+    }else{
+        mFilter = QRegularExpression();
+    }
     invalidateFilter();
 }
 
 bool MappingTreeProxy::filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const{
-    if(mFilter.isEmpty()){
+    if(mFilter == QRegularExpression()){
         return true;
     }
     QModelIndex nameIdx = sourceModel()->index(sourceRow, MappingTreeModel::Name, sourceParent);