Limit searches at 500 per page

* 5000 search results in a single page is too many to be useful and
  just results in a slow page load. If you need that many results use
  the API.
* Adds new parameter to WebRequest::getLimitOffset() to allow making
  the 5000 limit configurable by callers

Change-Id: I7c12e4b0526db6453aaba5d589ee1c01a54b72d4