Screen Resources page for dead links

[mekline]

Need to review this page (https://lookit.readthedocs.io/en/develop/other-learning-materials.html) for dead links and out-of-date resources.

For any dead links discovered, should do a quick google search for a replacement link, or add the text "DEAD LINK" in the PR for Melissa to review identify replacement resources.

[ec6wellesley]

@mekline I'm not quite sure how you would like me to make a PR when I found a dead link that I can't find a replacement for, such as the following:

Feel free to fill out the survey collecting info about what people would do with Lookit

3-year plan

If you would like I can make edits to the file and create a PR from that?