qt: Add generic flag support for keylistjobs
* lang/qt/src/keylistjob.h (addMode): New. * lang/qt/src/qgpgmekeylistjob.h (addMode): New. * lang/qt/src/qgpgmekeylistjob.cpp (addMode: New.
Instead of new API for each new thing lets be a bit more
generic / open.