Add pagination information to the /api/packages/ call

This is particularly useful when querying with acls=True which is slow as hell and even
hangs when asked to list too many packages. Using the pagination information, one
may iterate to retrieve all the information instead of doing it in a single call that crashes.
Change default of /api/packagers to return the list of all packagers if no pattern is provided
Make the page returned in the json an integer, otherwise the search would have failed