Add showCount option to hide other links JS

Allows specification of number of links that should be shown.
Hide all but first org on attachment preview

Shows an "and X others" link similar to document metadata.

https://www.pivotaltracker.com/story/show/61795800
Merge pull request #1203 from alphagov/61795800-cope-better-with-multiple-orgs-on-csv-preview

Hide all but first org on attachment preview