add InteractiveShell.display_page config

sends all pager output to regular output instead of pager

pagers are registered via the already-existing show_in_pager hook,
rather than clobbering like we used to do in `install_payload_page`
remove duplicate max(0, start) in pager_page
Merge pull request #7009 from minrk/pinfo-no-page

add InteractiveShell.display_page config