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
Delete unused step definitions

Running cucumber with the "-f stepdefs" flag will output all the step
definitions, outlining how long they took. This can be used to
identify the steps that are never run.

Note: only useful on a single-process test run as the steps will get
counted separately in a parallel test run, so the numbers will be out.
Re-implement date comparison with Rails date helpers
Merge pull request #737 from alphagov/hide-fewer-other-links

Hide fewer other links in document metadata

https://www.pivotaltracker.com/story/show/53629007
Merge pull request #740 from alphagov/delete-unused-steps

Delete unused step definitions
Merge pull request #741 from alphagov/date-comparison-helpers

Re-implement date comparison with Rails date helpers