Merge branch 'issue/virtual_override_final' into 'develop'

use exactly one of virtual, override, or final.

See merge request !86
4 jobs for develop
Status Job ID Name Coverage
  Test
canceled #8545
debian:10 clang-6-libcpp-17

canceled #8544
debian:10 gcc-8-17

canceled #8546
debian:9 gcc-6-14

canceled #8547
ubuntu:18.04 clang-6-17