Hide fewer other links in document metadata

js-hide-other-links won't hide 2 or fewer links if they're
reasonably short. Stops "Something + 1 other" showing in the
metadata when the 1 other thing is really short.
Add tests for hiding long links
Merge pull request #737 from alphagov/hide-fewer-other-links

Hide fewer other links in document metadata

https://www.pivotaltracker.com/story/show/53629007