Feature/add card behavior

Hides the current card view when adding a card and refactored the JS into a separate module.

@jazahn please review

Note: I branched off of [PR 37](https://github.com/Harvard-ATG/HarvardCards/pull/37), so it includes those changes as well.

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Jira: [FLASH-49](https://jira.huit.harvard.edu/browse/FLASH-49)