Add scientific notation filter

[munnsmunns]

Add a template filter that formats floats in scientific notation when <=1e-5 or >1e5, and use that filter when displaying assessment values.

[rabstejnek]

Looks good! I had one comment for you to address, which may result in updating the code documentation to be more clear about the behavior or changing the template filter to ignore large values.

[shapiromatron]

Made a stylistic change to the filter itself, and did more work on the tests, so it self-documents what this filter returns.

[shapiromatron]

this makes it very clear what this filter does. I'd recommend doing something like this in the future so there's no ambiguity in what the filter looks like.