Split ShouldContain into AnyShouldContain and AllShouldContain

The current `ShouldContain` extension method for `QueryWrapper` asserts that all elements contains the expected value, but you might also want to assert that any of the elements in the query contains the value. This PR renames the existing method to `AllShouldContain` and adds another method `AnyShouldContain`.

This should make @jchannon happy :wink: