This is corresponding dotherside part of the issue 1725.
So far we had kind of a memory leak, cause objects added to the filter were not
deleted ever. When the app is closing, it just removes filters, but doesn't
delete them.
I faced a logical issue, that we were sending qmlengine pointer to the
installEventFilter method, instead object which may or may not rely on the
qqmlengine instance, that is fixed also.
Fixes: #1725
B.Melnik
Sale Djenic
Alexandra Betouni
Andrei Smirnov
B.Melnik
Richard Ramos
Ștefan Talpalaru
Michał Cieślak