Adopting SailfishOS code to recent changes in desktop code

• Generation of logging_*.{cpp,h} happens in desktop code in build directory via special CMake code provided by ECM. Re-creating those logging files for QMake-based builds requires manually invoking shell script generate-logging-categories.sh
• Migrating to enum constants instead of QString for search forms' values as introduced in commit 497886ebc40442f367.
• Adding missing #include statement.
• Include DBus headers only if code making use of those headers is actually compiled (code is behind #ifdef HAVE_KF5, same should be for #include).