Allow 500 relays shown per page

Given that we bumped the max limit of relays run on a single IP address from 2 to 8 a while ago, large families got even bigger over time. Sometimes it's cumbersome to have only 100 relays shown per page (the max amount after 10, 25, 50) and it would be nice to be able to show 500 per page instead.

Reported as a feature request by JN.