Create `AllElements`

[sylvainhalle]

Yet another exhaustive picker, which this time enumerates all the elements of a collection --a set, a list or an array-- with and without the scramble option.

Example:

AllElements<Integer> p1 = new AllElements<Integer>(true, 3, 1, 4, 5); // true is the scramble flag

Set<String> set = new HashSet<String>();
set.add("a"); set.add("b"); set.add("c");
AllElements<String> p2 = new AllElements<String>(set);

Hint: implement as a descendant of Playback.