Feature/add collection with template preview

This PR adds functionality to the *Add Course* view so that when the user selects a card template, they will see a preview of what it looks like.

@jazahn please review

**Note:** branched off of [pull request 33](https://github.com/Harvard-ATG/HarvardCards/pull/33) so please review and merge that one first, then review this since it includes those changes, at least until they're merged into dev.