feature/reveal-card-downarrow

This PR adds the ability to reveal or hide the card using the up/down arrow keys. As a result of this feature, the user should now be able to navigate using left/right arrow keys and hide/reveal using up/down arrow keys.

Note that the flip mode functionality broke the reveal button, so I refactored the html to fix that (moved the css classes used by flip mode into the card fields template).

@jazahn can you review this and merge into dev if it looks good?

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[FLASH-129](https://jira.huit.harvard.edu/browse/FLASH-129)