Limit the number of questions asked per visit

[Teester]

I have noticed that POIs with large numbers of questions can become a bit annoying to answer. Miller's Law (https://en.wikipedia.org/wiki/Miller%27s_law) suggests that the number of objects an average person can hold in working memory is about seven.

The number of questions asked per session should be limited to 7. The largest number at the moment is amenity=restaurant with 15 questions. Questions should be asked according to the following hierarchy:

1. A random selection of unanswered questions
2. If there are less than 7 unanswered questions, then a random selection of already answered questions should make up the remainder.
3. The selected questions should then be randomized so that they are not presented in the same order every time.