Set CXX min version to C++11, fix of warnings
Summary:
Set CXX min version to C++11, fix of warnings
- Add override to virtual functions where needed
- Add static to functions wthout definition
- Replace 0 with nullptr where needed
Test Plan: Just cleaned up code, no changes yet
Reviewers: hein
Reviewed By: hein
Subscribers: apol
Differential Revision: https://phabricator.kde.org/D8520