Use `merge: true` by default for Collection.reset. Ref #320
Simpler test added for `merge: true` on Collection.reset.

Revert "Merge pull request #320 from elasticsales/collection-set-vs-reset"

This reverts commit c31ea90071753f1f475f780ef4143229d5a28f19, reversing
changes made to 9b52eb220bb86a2da5e41c08e55b76a1f2108871.