Use simple Next/Prev paging for CI Jobs page
This changes the pagination system of the "Jobs" page so we don't need to perform expensive COUNT queries.
@tauriedavis @sarrahvesselov This is based SQL timings of up to 14s for the count query. We could do this for only the "All" and "Finished" tabs but we want to get this in for 10.4 and that would take longer. Also that might be more confusing to users and in any case for the list of CI jobs which is a very dynamic list it seems unlikely users navigate by page number anyways.
This is following the same pattern as https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13456 and will have the same appearance.
Edited by Gregory Stark