Build mediascanner2 for focal

• Fix sizeof call to avoid crashing.
• Migrate directory reading code to c++17.
• Remove Ubuntu namespacing of QML module.
• Fix strftime format warning.
• Add missing build depends on libbost-dev.
• Use std::filesystem::remove_all to fix test build.
• Remove superfluous std::move to fix test build.
• Move Jenkinsfile to debian directory.
• Migrate bzrignore to gitignore.

This fixes #3 (closed).