ui/gtk3: Sort Unicode candidates
ui/gtk3: Sort Unicode candidates

BUG=rhbz#1554714
R=Shawn.P.Huang@gmail.com

Review URL: https://codereview.appspot.com/339430043

ibus/ibus,ibus/ibus,fujiwarat/ibus,fujiwarat/ibus,fujiwarat/ibus,ibus/ibus,ibus/ibus,fujiwarat/ibus