Create new exercise for sorting with multiple columns

[bencomp]

The last exercise in episode 3, on sorting the data by GPS coordinates, is bound to be changed (as discussed in #43). I suggest to create a new exercise to practice sorting by multiple columns.

I also ask to find the correct name for village 49 only using interview dates. That makes the exercise in episode 3 smaller and quicker, although it removes the need for sorting on multiple columns. Maybe we can add an exercise with sorting on multiple values for finding errors in the ward and district columns?

Originally posted by @bencomp in #43 (comment)