GIFs behave inconsistently on experimenter vs. home view

[mekline]

Description This study displays a broken link on both the search page and the preview-study page:

https://lookit.mit.edu/studies/1e6c0129-13c7-4736-91af-e8886f2b24cd/

However, the corresponding experimenter view displays the GIF, which is presumably why it was never flagged during creation or review:

https://lookit.mit.edu/exp/studies/1876/

How to reproduce Check links above!

Expected behavior GIFs should either work on all views, or else be rejected at the study creation/edit forms

Screenshots

Environment (OS, browser, branch, etc.):

Chrome, Mac laptop

[okaycj]

The study linked in the issue no longer uses gif to encode its images. This should still be looked into though.