pagination consistency

[davidism]

Pagination has a few defaults that we might want to adjust, and 3.0 is the time to do it.

• per_page can be 0. I'm not sure why this is allowed. page cannot be 0, that causes a 404 error.
• max_per_page should have a default, maybe 100, so projects don't need to remember to add one to prevent users passing very high values.
• pages is currently 0 instead of None if total is None. If the total is 0, 0 pages makes sense, but if the total wasn't calculated it doesn't mean there are 0 pages it just means we don't know the number.

[davidism]

Decided not to change pages if total is None. It keeps the type simple (int), and would require the same amount of user code to check if page.total is None instead of if page.pages is None.