Add task search backend.
Add task search backend.

For https://unisubs.sifterapp.com/projects/12298/issues/511750/comments

ujdhesa/unisubs,norayr/unisubs,pculture/unisubs,norayr/unisubs,wevoice/wesub,ofer43211/unisubs,eloquence/unisubs,wevoice/wesub,ofer43211/unisubs,ujdhesa/unisubs,eloquence/unisubs,ofer43211/unisubs,ReachingOut/unisubs,ReachingOut/unisubs,pculture/unisubs,ReachingOut/unisubs,ReachingOut/unisubs,pculture/unisubs,ujdhesa/unisubs,eloquence/unisubs,norayr/unisubs,wevoice/wesub,eloquence/unisubs,wevoice/wesub,ujdhesa/unisubs,pculture/unisubs,norayr/unisubs,ofer43211/unisubs