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/mappingdata.cpp b/mappingdata.cpp
index d2e061a..3253b2d 100644
--- a/mappingdata.cpp
+++ b/mappingdata.cpp
@@ -11,7 +11,7 @@
 
 MappingData::MappingData() : mappingId(-1), descId(-1) {}
 
-bool MappingData::operator ==(const MappingData &other){
+bool MappingData::operator ==(const MappingData &other) const{
     bool retval = (
                     mappingId == other.mappingId &&
                     descId == other.descId &&