Point Of Interest (Quest Details etc.)

@wsuchy , @jacekjursza and me - decided to implement QuestDetails API and NearbyQuests API (+ all related stuff) in single brunch (because these tasks are strongly coupled).

At the moment - this pull request must be only reviewed and not merged!
Since it's going to contain integers, maybe it'd be useful could take a look at #4306 , abstract and reuse both there and here?