Kh - Lots of general UI fixes/additions

Added informational dialogs on db update and regular export/import
completion.
Changed selection mode for regular import/export dialogs to extended
(matches what is usually considered "normal" selection mode for most
users)
Regular import "importing" informational dialog now updates to show
which singer is being imported.
Regular export will no longer prompt for filename when no singer has
been selected and export buttons are pushed.