Fix People search for large result sets

* Prevents `Request URI too long` error on App Engine when querying for
  hundreds of IDs.
* Use `{{#each list}}` instead of `{{#list}}` to avoid rerendering the
  entire list for new pages (required a fix in `person_roles` mustache
  helper).
* Make "View More" change to "All results shown" when there are no more
  pages to display
* Fix styling of "View More" buttons

Doesn't yet handle paging of search results, but it doesn't cause the Request URI failure.